all: fix broken docunits
[nit.git] / lib / standard / string.nit
index e92fea8..62d5ddc 100644 (file)
 module string
 
 import math
-intrude import collection # FIXME should be collection::array
+import collection
+intrude import collection::array
 
 `{
 #include <stdio.h>
+#include <string.h>
 `}
 
 ###############################################################################
 # String                                                                      #
 ###############################################################################
 
-# Common subclass for String and Buffer
-abstract class AbstractString
-       super AbstractArrayRead[Char]
+# High-level abstraction for all text representations
+abstract class Text
+       super Comparable
 
-       readable private var _items: NativeString
+       redef type OTHER: Text
 
-       fun chars: StringCharView is abstract
+       # Type of self (used for factorization of several methods, ex : substring_from, empty...)
+       type SELFTYPE: Text
 
-       # Access a character at `index` in the string.
+       # Gets a view on the chars of the Text object
        #
-       #     assert "abcd"[2]         == 'c'
-       redef fun [](index) do return _items[index]
+       #     assert "hello".chars.to_a == ['h', 'e', 'l', 'l', 'o']
+       fun chars: SequenceRead[Char] is abstract
+
+       # Number of characters contained in self.
+       #
+       #     assert "12345".length == 5
+       #     assert "".length == 0
+       fun length: Int is abstract
 
        # Create a substring.
        #
@@ -48,24 +57,111 @@ abstract class AbstractString
        # A `from` index < 0 will be replaced by 0.
        # Unless a `count` value is > 0 at the same time.
        # In this case, `from += count` and `count -= from`.
-       fun substring(from: Int, count: Int): String
+       fun substring(from: Int, count: Int): SELFTYPE is abstract
+
+       # Iterates on the substrings of self if any
+       fun substrings: Iterator[Text] is abstract
+
+       # Is the current Text empty (== "")
+       #
+       #     assert "".is_empty
+       #     assert not "foo".is_empty
+       fun is_empty: Bool do return self.length == 0
+
+       # Returns an empty Text of the right type
+       #
+       # This method is used internally to get the right
+       # implementation of an empty string.
+       protected fun empty: SELFTYPE is abstract
+
+       # Gets the first char of the Text
+       #
+       # DEPRECATED : Use self.chars.first instead
+       fun first: Char do return self.chars[0]
+
+       # Access a character at `index` in the string.
+       #
+       #     assert "abcd"[2]         == 'c'
+       #
+       # DEPRECATED : Use self.chars.[] instead
+       fun [](index: Int): Char do return self.chars[index]
+
+       # Gets the index of the first occurence of 'c'
+       #
+       # Returns -1 if not found
+       #
+       # DEPRECATED : Use self.chars.index_of instead
+       fun index_of(c: Char): Int
        do
-               assert count >= 0
-               count += from
-               if from < 0 then from = 0
-               if count > length then count = length
-               if from < count then
-                       var r = new Buffer.with_capacity(count - from)
-                       while from < count do
-                               r.chars.push(_items[from])
-                               from += 1
-                       end
-                       return r.to_s
-               else
-                       return ""
+               return index_of_from(c, 0)
+       end
+
+       # Gets the last char of self
+       #
+       # DEPRECATED : Use self.chars.last instead
+       fun last: Char do return self.chars[length-1]
+
+       # Gets the index of the first occurence of ´c´ starting from ´pos´
+       #
+       # Returns -1 if not found
+       #
+       # DEPRECATED : Use self.chars.index_of_from instead
+       fun index_of_from(c: Char, pos: Int): Int
+       do
+               var iter = self.chars.iterator_from(pos)
+               while iter.is_ok do
+                       if iter.item == c then return iter.index
+                       iter.next
+               end
+               return -1
+       end
+
+       # Gets the last index of char ´c´
+       #
+       # Returns -1 if not found
+       #
+       # DEPRECATED : Use self.chars.last_index_of instead
+       fun last_index_of(c: Char): Int
+       do
+               return last_index_of_from(c, length - 1)
+       end
+
+       # Return a null terminated char *
+       fun to_cstring: NativeString do return flatten.to_cstring
+
+       # The index of the last occurrence of an element starting from pos (in reverse order).
+       #
+       #     var s = "/etc/bin/test/test.nit"
+       #     assert s.last_index_of_from('/', s.length-1) == 13
+       #     assert s.last_index_of_from('/', 12)         == 8
+       #
+       # Returns -1 if not found
+       #
+       # DEPRECATED : Use self.chars.last_index_of_from instead
+       fun last_index_of_from(item: Char, pos: Int): Int
+       do
+               var iter = self.chars.reverse_iterator_from(pos)
+               while iter.is_ok do
+                       if iter.item == item then return iter.index
+                       iter.next
                end
+               return -1
+       end
+
+       # Gets an iterator on the chars of self
+       #
+       # DEPRECATED : Use self.chars.iterator instead
+       fun iterator: Iterator[Char]
+       do
+               return self.chars.iterator
        end
 
+
+       # Gets an Array containing the chars of self
+       #
+       # DEPRECATED : Use self.chars.to_a instead
+       fun to_a: Array[Char] do return chars.to_a
+
        # Create a substring from `self` beginning at the `from` position
        #
        #     assert "abcd".substring_from(1)    ==  "bcd"
@@ -73,9 +169,10 @@ abstract class AbstractString
        #     assert "abcd".substring_from(2)    ==  "cd"
        #
        # As with substring, a `from` index < 0 will be replaced by 0
-       fun substring_from(from: Int): String
+       fun substring_from(from: Int): SELFTYPE
        do
-               assert from < length
+               if from >= self.length then return empty
+               if from < 0 then from = 0
                return substring(from, length - from)
        end
 
@@ -83,20 +180,33 @@ abstract class AbstractString
        #
        #     assert "abcd".has_substring("bc",1)            ==  true
        #     assert "abcd".has_substring("bc",2)            ==  false
+       #
+       # Returns true iff all characters of `str` are presents
+       # at the expected index in `self.`
+       # The first character of `str` being at `pos`, the second
+       # character being at `pos+1` and so on...
+       #
+       # This means that all characters of `str` need to be inside `self`.
+       #
+       #     assert "abcd".has_substring("xab", -1)         == false
+       #     assert "abcd".has_substring("cdx", 2)          == false
+       #
+       # And that the empty string is always a valid substring.
+       #
+       #     assert "abcd".has_substring("", 2)             == true
+       #     assert "abcd".has_substring("", 200)           == true
        fun has_substring(str: String, pos: Int): Bool
        do
-               var itsindex = str.length - 1
-               var myindex = pos + itsindex
-               var myitems = _items
-               var itsitems = str._items
-               if myindex > length or itsindex > myindex  then return false
-               var its_index_from = str._index_from
-               itsindex += its_index_from
-               while itsindex >= its_index_from do
-                       if myitems[myindex] != itsitems[itsindex] then return false
-                       myindex -= 1
-                       itsindex -= 1
+               if str.is_empty then return true
+               if pos < 0 or pos + str.length > length then return false
+               var myiter = self.chars.iterator_from(pos)
+               var itsiter = str.chars.iterator
+               while myiter.is_ok and itsiter.is_ok do
+                       if myiter.item != itsiter.item then return false
+                       myiter.next
+                       itsiter.next
                end
+               if itsiter.is_ok then return false
                return true
        end
 
@@ -135,6 +245,8 @@ abstract class AbstractString
        end
 
        # If `self` contains only digits and alpha <= 'f', return the corresponding integer.
+       #
+       #     assert "ff".to_hex == 255
        fun to_hex: Int do return a_to(16)
 
        # If `self` contains only digits and letters, return the corresponding integer in a given base
@@ -145,8 +257,8 @@ abstract class AbstractString
                var i = 0
                var neg = false
 
-               for c in self.chars
-               do
+               for j in [0..length[ do
+                       var c = chars[j]
                        var v = c.to_i
                        if v > base then
                                if neg then
@@ -176,12 +288,10 @@ abstract class AbstractString
        fun is_numeric: Bool
        do
                var has_point_or_comma = false
-               for i in self.chars
-               do
-                       if not i.is_numeric
-                       then
-                               if (i == '.' or i == ',') and not has_point_or_comma
-                               then
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if not c.is_numeric then
+                               if (c == '.' or c == ',') and not has_point_or_comma then
                                        has_point_or_comma = true
                                else
                                        return false
@@ -191,24 +301,81 @@ abstract class AbstractString
                return true
        end
 
-       # A upper case version of `self`
+       # Returns `true` if the string contains only Hex chars
        #
-       #     assert "Hello World!".to_upper     == "HELLO WORLD!"
-       fun to_upper: String
+       #     assert "048bf".is_hex  == true
+       #     assert "ABCDEF".is_hex  == true
+       #     assert "0G".is_hex == false
+       fun is_hex: Bool
+       do
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if not (c >= 'a' and c <= 'f') and
+                          not (c >= 'A' and c <= 'F') and
+                          not (c >= '0' and c <= '9') then return false
+               end
+               return true
+       end
+
+       # Are all letters in `self` upper-case ?
+       #
+       #     assert "HELLO WORLD".is_upper == true
+       #     assert "%$&%!".is_upper       == true
+       #     assert "hello world".is_upper == false
+       #     assert "Hello World".is_upper == false
+       fun is_upper: Bool
+       do
+               for i in [0..length[ do
+                       var char = chars[i]
+                       if char.is_lower then return false
+               end
+               return true
+       end
+
+       # Are all letters in `self` lower-case ?
+       #
+       #     assert "hello world".is_lower == true
+       #     assert "%$&%!".is_lower       == true
+       #     assert "Hello World".is_lower == false
+       fun is_lower: Bool
+       do
+               for i in [0..length[ do
+                       var char = chars[i]
+                       if char.is_upper then return false
+               end
+               return true
+       end
+                       
+       # Removes the whitespaces at the beginning of self
+       #
+       #     assert " \n\thello \n\t".l_trim == "hello \n\t"
+       #
+       # A whitespace is defined as any character which ascii value is less than or equal to 32
+       fun l_trim: SELFTYPE
        do
-               var s = new Buffer.with_capacity(length)
-               for i in self.chars do s.add(i.to_upper)
-               return s.to_s
+               var iter = self.chars.iterator
+               while iter.is_ok do
+                       if iter.item.ascii > 32 then break
+                       iter.next
+               end
+               if iter.index == length then return self.empty
+               return self.substring_from(iter.index)
        end
 
-       # A lower case version of `self`
+       # Removes the whitespaces at the end of self
        #
-       #     assert "Hello World!".to_lower     == "hello world!"
-       fun to_lower : String
+       #     assert " \n\thello \n\t".r_trim == " \n\thello"
+       #
+       # A whitespace is defined as any character which ascii value is less than or equal to 32
+       fun r_trim: SELFTYPE
        do
-               var s = new Buffer.with_capacity(length)
-               for i in self.chars do s.add(i.to_lower)
-               return s.to_s
+               var iter = self.chars.reverse_iterator
+               while iter.is_ok do
+                       if iter.item.ascii > 32 then break
+                       iter.next
+               end
+               if iter.index < 0 then return self.empty
+               return self.substring(0, iter.index + 1)
        end
 
        # Trims trailing and preceding white spaces
@@ -216,39 +383,42 @@ abstract class AbstractString
        #
        #     assert "  Hello  World !  ".trim   == "Hello  World !"
        #     assert "\na\nb\tc\t".trim          == "a\nb\tc"
-       fun trim: String
-       do
-               if self.length == 0 then return self.to_s
-               # find position of the first non white space char (ascii < 32) from the start of the string
-               var start_pos = 0
-               while self.chars[start_pos].ascii <= 32 do
-                       start_pos += 1
-                       if start_pos == length then return ""
-               end
-               # find position of the first non white space char from the end of the string
-               var end_pos = length - 1
-               while self.chars[end_pos].ascii <= 32 do
-                       end_pos -= 1
-                       if end_pos == start_pos then return self.chars[start_pos].to_s
-               end
-               return self.substring(start_pos, end_pos - start_pos + 1)
-       end
+       fun trim: SELFTYPE do return (self.l_trim).r_trim
 
-       redef fun output
+       # Justify a self in a space of `length`
+       #
+       # `left` is the space ratio on the left side.
+       # * 0.0 for left-justified (no space at the left)
+       # * 1.0 for right-justified (all spaces at the left)
+       # * 0.5 for centered (half the spaces at the left)
+       #
+       #     assert "hello".justify(10, 0.0)  == "hello     "
+       #     assert "hello".justify(10, 1.0)  == "     hello"
+       #     assert "hello".justify(10, 0.5)  == "  hello   "
+       #
+       # If `length` is not enough, `self` is returned as is.
+       #
+       #     assert "hello".justify(2, 0.0)   == "hello"
+       #
+       # REQUIRE: left >= 0.0 and left <= 1.0
+       # ENSURE: `self.length <= length implies result.length == length`
+       # ENSURE: `self.length >= length implies result == self
+       fun justify(length: Int, left: Float): SELFTYPE
        do
-               var i = 0
-               while i < length do
-                       _items[i].output
-                       i += 1
-               end
+               var diff = length - self.length
+               if diff <= 0 then return self
+               assert left >= 0.0 and left <= 1.0
+               var before = (diff.to_f * left).to_i
+               return " " * before + self + " " * (diff-before)
        end
 
        # Mangle a string to be a unique string only made of alphanumeric characters
        fun to_cmangle: String
        do
-               var res = new Buffer
+               var res = new FlatBuffer
                var underscore = false
-               for c in self.chars do
+               for i in [0..length[ do
+                       var c = chars[i]
                        if (c >= 'a' and c <= 'z') or (c >='A' and c <= 'Z') then
                                res.add(c)
                                underscore = false
@@ -280,8 +450,9 @@ abstract class AbstractString
        #     assert "\n\"'\\".escape_to_c         == "\\n\\\"\\'\\\\"
        fun escape_to_c: String
        do
-               var b = new Buffer
-               for c in self.chars do
+               var b = new FlatBuffer
+               for i in [0..length[ do
+                       var c = chars[i]
                        if c == '\n' then
                                b.append("\\n")
                        else if c == '\0' then
@@ -307,9 +478,9 @@ abstract class AbstractString
        #     assert "ab|\{\}".escape_more_to_c("|\{\}") == "ab\\|\\\{\\\}"
        fun escape_more_to_c(chars: String): String
        do
-               var b = new Buffer
-               for c in escape_to_c do
-                       if chars.has(c) then
+               var b = new FlatBuffer
+               for c in escape_to_c.chars do
+                       if chars.chars.has(c) then
                                b.add('\\')
                        end
                        b.add(c)
@@ -317,24 +488,68 @@ abstract class AbstractString
                return b.to_s
        end
 
-       # Escape to c plus braces
+       # Escape to C plus braces
        #
        #     assert "\n\"'\\\{\}".escape_to_nit      == "\\n\\\"\\'\\\\\\\{\\\}"
        fun escape_to_nit: String do return escape_more_to_c("\{\}")
 
+       # Escape to POSIX Shell (sh).
+       #
+       # Abort if the text contains a null byte.
+       #
+       #     assert "\n\"'\\\{\}0".escape_to_sh == "'\n\"'\\''\\\{\}0'"
+       fun escape_to_sh: String do
+               var b = new FlatBuffer
+               b.chars.add '\''
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if c == '\'' then
+                               b.append("'\\''")
+                       else
+                               assert without_null_byte: c != '\0'
+                               b.add(c)
+                       end
+               end
+               b.chars.add '\''
+               return b.to_s
+       end
+
+       # Escape to include in a Makefile
+       #
+       # Unfortunately, some characters are not escapable in Makefile.
+       # These characters are `;`, `|`, `\`, and the non-printable ones.
+       # They will be rendered as `"?{hex}"`.
+       fun escape_to_mk: String do
+               var b = new FlatBuffer
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if c == '$' then
+                               b.append("$$")
+                       else if c == ':' or c == ' ' or c == '#' then
+                               b.add('\\')
+                               b.add(c)
+                       else if c.ascii < 32 or c == ';' or c == '|' or c == '\\' or c == '=' then
+                               b.append("?{c.ascii.to_base(16, false)}")
+                       else
+                               b.add(c)
+                       end
+               end
+               return b.to_s
+       end
+
        # Return a string where Nit escape sequences are transformed.
        #
-       # Example:
        #     var s = "\\n"
        #     assert s.length        ==  2
        #     var u = s.unescape_nit
        #     assert u.length        ==  1
-       #     assert u[0].ascii      ==  10 # (the ASCII value of the "new line" character)
+       #     assert u.chars[0].ascii      ==  10 # (the ASCII value of the "new line" character)
        fun unescape_nit: String
        do
-               var res = new Buffer.with_capacity(self.length)
+               var res = new FlatBuffer.with_capacity(self.length)
                var was_slash = false
-               for c in self do
+               for i in [0..length[ do
+                       var c = chars[i]
                        if not was_slash then
                                if c == '\\' then
                                        was_slash = true
@@ -358,39 +573,223 @@ abstract class AbstractString
                end
                return res.to_s
        end
-end
 
-# Abstract class for the SequenceRead compatible
-# views on String and Buffer objects
-abstract class StringCharView
-       super SequenceRead[Char]
+       # Encode `self` to percent (or URL) encoding
+       #
+       #     assert "aBc09-._~".to_percent_encoding == "aBc09-._~"
+       #     assert "%()< >".to_percent_encoding == "%25%28%29%3c%20%3e"
+       #     assert ".com/post?e=asdf&f=123".to_percent_encoding == ".com%2fpost%3fe%3dasdf%26f%3d123"
+       fun to_percent_encoding: String
+       do
+               var buf = new FlatBuffer
+
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if (c >= '0' and c <= '9') or
+                          (c >= 'a' and c <= 'z') or
+                          (c >= 'A' and c <= 'Z') or
+                          c == '-' or c == '.' or
+                          c == '_' or c == '~'
+                       then
+                               buf.add c
+                       else buf.append "%{c.ascii.to_hex}"
+               end
+
+               return buf.to_s
+       end
+
+       # Decode `self` from percent (or URL) encoding to a clear string
+       #
+       # Replace invalid use of '%' with '?'.
+       #
+       #     assert "aBc09-._~".from_percent_encoding == "aBc09-._~"
+       #     assert "%25%28%29%3c%20%3e".from_percent_encoding == "%()< >"
+       #     assert ".com%2fpost%3fe%3dasdf%26f%3d123".from_percent_encoding == ".com/post?e=asdf&f=123"
+       #     assert "%25%28%29%3C%20%3E".from_percent_encoding == "%()< >"
+       #     assert "incomplete %".from_percent_encoding == "incomplete ?"
+       #     assert "invalid % usage".from_percent_encoding == "invalid ? usage"
+       fun from_percent_encoding: String
+       do
+               var buf = new FlatBuffer
+
+               var i = 0
+               while i < length do
+                       var c = chars[i]
+                       if c == '%' then
+                               if i + 2 >= length then
+                                       # What follows % has been cut off
+                                       buf.add '?'
+                               else
+                                       i += 1
+                                       var hex_s = substring(i, 2)
+                                       if hex_s.is_hex then
+                                               var hex_i = hex_s.to_hex
+                                               buf.add hex_i.ascii
+                                               i += 1
+                                       else
+                                               # What follows a % is not Hex
+                                               buf.add '?'
+                                               i -= 1
+                                       end
+                               end
+                       else buf.add c
+
+                       i += 1
+               end
 
-       type SELFTYPE: AbstractString
+               return buf.to_s
+       end
+
+       # Escape the four characters `<`, `>`, `&`, and `"` with their html counterpart
+       #
+       #     assert "a&b->\"x\"".html_escape      ==  "a&amp;b-&gt;&quot;x&quot;"
+       fun html_escape: SELFTYPE
+       do
+               var buf = new FlatBuffer
+
+               for i in [0..length[ do
+                       var c = chars[i]
+                       if c == '&' then
+                               buf.append "&amp;"
+                       else if c == '<' then
+                               buf.append "&lt;"
+                       else if c == '>' then
+                               buf.append "&gt;"
+                       else if c == '"' then
+                               buf.append "&quot;"
+                       else buf.add c
+               end
 
-       private var target: SELFTYPE
+               return buf.to_s
+       end
 
-       private init(tgt: SELFTYPE)
+       # Equality of text
+       # Two pieces of text are equals if thez have the same characters in the same order.
+       #
+       #     assert "hello" == "hello"
+       #     assert "hello" != "HELLO"
+       #     assert "hello" == "hel"+"lo"
+       #
+       # Things that are not Text are not equal.
+       #
+       #     assert "9" != '9'
+       #     assert "9" != ['9']
+       #     assert "9" != 9
+       #
+       #     assert "9".chars.first == '9'   # equality of Char
+       #     assert "9".chars       == ['9'] # equality of Sequence
+       #     assert "9".to_i        == 9     # equality of Int
+       redef fun ==(o)
        do
-               target = tgt
+               if o == null then return false
+               if not o isa Text then return false
+               if self.is_same_instance(o) then return true
+               if self.length != o.length then return false
+               return self.chars == o.chars
        end
 
-       redef fun is_empty do return target.is_empty
+       # Lexicographical comparaison
+       #
+       #     assert "abc" < "xy"
+       #     assert "ABC" < "abc"
+       redef fun <(other)
+       do
+               var self_chars = self.chars.iterator
+               var other_chars = other.chars.iterator
 
-       redef fun length do return target.length
+               while self_chars.is_ok and other_chars.is_ok do
+                       if self_chars.item < other_chars.item then return true
+                       if self_chars.item > other_chars.item then return false
+                       self_chars.next
+                       other_chars.next
+               end
+
+               if self_chars.is_ok then
+                       return false
+               else
+                       return true
+               end
+       end
 
-       redef fun has(c: Char): Bool
+       # Escape string used in labels for graphviz
+       #
+       #   assert ">><<".escape_to_dot == "\\>\\>\\<\\<"
+       fun escape_to_dot: String
+       do
+               return escape_more_to_c("|\{\}<>")
+       end
+
+       # Flat representation of self
+       fun flatten: FlatText is abstract
+
+       private var hash_cache: nullable Int = null
+
+       redef fun hash
        do
-               for i in self do
-                       if i == c then return true
+               if hash_cache == null then
+                       # djb2 hash algorithm
+                       var h = 5381
+
+                       for i in [0..length[ do
+                               var char = chars[i]
+                               h = h.lshift(5) + h + char.ascii
+                       end
+
+                       hash_cache = h
                end
-               return false
+               return hash_cache.as(not null)
        end
 
 end
 
+# All kinds of array-based text representations.
+abstract class FlatText
+       super Text
+
+       # Underlying C-String (`char*`)
+       #
+       # Warning : Might be void in some subclasses, be sure to check
+       # if set before using it.
+       private var items: NativeString is noinit
+
+       # Real items, used as cache for to_cstring is called
+       private var real_items: nullable NativeString = null
+
+       redef var length: Int = 0
+
+       redef fun output
+       do
+               var i = 0
+               while i < length do
+                       items[i].output
+                       i += 1
+               end
+       end
+
+       redef fun flatten do return self
+end
+
+# Abstract class for the SequenceRead compatible
+# views on String and Buffer objects
+private abstract class StringCharView
+       super SequenceRead[Char]
+
+       type SELFTYPE: Text
+
+       var target: SELFTYPE
+
+       redef fun is_empty do return target.is_empty
+
+       redef fun length do return target.length
+
+       redef fun iterator: IndexedIterator[Char] do return self.iterator_from(0)
+
+       redef fun reverse_iterator do return self.reverse_iterator_from(self.length - 1)
+end
+
 # View on Buffer objects, extends Sequence
 # for mutation operations
-abstract class BufferCharView
+private abstract class BufferCharView
        super StringCharView
        super Sequence[Char]
 
@@ -398,35 +797,220 @@ abstract class BufferCharView
 
 end
 
-# Immutable strings of characters.
-class String
-       super Comparable
-       super AbstractString
-       super StringCapable
+# A `String` holds and manipulates an arbitrary sequence of characters.
+#
+# String objects may be created using literals.
+#
+#     assert "Hello World!" isa String
+abstract class String
+       super Text
+
+       redef type SELFTYPE: String
+
+       redef fun to_s do return self
+
+       # Concatenates `o` to `self`
+       #
+       #     assert "hello" + "world"  == "helloworld"
+       #     assert "" + "hello" + ""  == "hello"
+       fun +(o: Text): SELFTYPE is abstract
+
+       # Concatenates self `i` times
+       #
+       #     assert "abc" * 4 == "abcabcabcabc"
+       #     assert "abc" * 1 == "abc"
+       #     assert "abc" * 0 == ""
+       fun *(i: Int): SELFTYPE is abstract
+
+       # Insert `s` at `pos`.
+       #
+       #     assert "helloworld".insert_at(" ", 5)     == "hello world"
+       fun insert_at(s: String, pos: Int): SELFTYPE is abstract
+
+       redef fun substrings: Iterator[String] is abstract
+
+       # Returns a reversed version of self
+       #
+       #     assert "hello".reversed  == "olleh"
+       #     assert "bob".reversed    == "bob"
+       #     assert "".reversed       == ""
+       fun reversed: SELFTYPE is abstract
+
+       # A upper case version of `self`
+       #
+       #     assert "Hello World!".to_upper     == "HELLO WORLD!"
+       fun to_upper: SELFTYPE is abstract
+
+       # A lower case version of `self`
+       #
+       #     assert "Hello World!".to_lower     == "hello world!"
+       fun to_lower : SELFTYPE is abstract
+
+       # Takes a camel case `self` and converts it to snake case 
+       #
+       #     assert "randomMethodId".to_snake_case == "random_method_id"
+       #
+       # If `self` is upper, it is returned unchanged
+       #
+       #     assert "RANDOM_METHOD_ID".to_snake_case == "RANDOM_METHOD_ID"
+       #
+       # If the identifier is prefixed by an underscore, the underscore is ignored
+       #
+       #     assert "_privateField".to_snake_case == "_private_field"
+       fun to_snake_case: SELFTYPE
+       do
+               if self.is_upper then return self
+
+               var new_str = new FlatBuffer.with_capacity(self.length)
+               var is_first_char = true
+
+               for i in [0..length[ do
+                       var char = chars[i]
+                       if is_first_char then 
+                               new_str.add(char.to_lower)
+                               is_first_char = false
+                       else if char.is_upper then
+                               new_str.add('_')
+                               new_str.add(char.to_lower)
+                       else
+                               new_str.add(char)
+                       end
+               end
+               
+               return new_str.to_s
+       end
+
+       # Takes a snake case `self` and converts it to camel case 
+       #
+       #     assert "random_method_id".to_camel_case == "randomMethodId"
+       #
+       # If the identifier is prefixed by an underscore, the underscore is ignored
+       #
+       #     assert "_private_field".to_camel_case == "_privateField"
+       #
+       # If `self` is upper, it is returned unchanged
+       #
+       #     assert "RANDOM_ID".to_camel_case == "RANDOM_ID"
+       #
+       # If there are several consecutive underscores, they are considered as a single one
+       #
+       #     assert "random__method_id".to_camel_case == "randomMethodId"
+       fun to_camel_case: SELFTYPE
+       do
+               if self.is_upper then return self
+
+               var new_str = new FlatBuffer
+               var is_first_char = true
+               var follows_us = false
+
+               for i in [0..length[ do
+                       var char = chars[i]
+                       if is_first_char then
+                               new_str.add(char)
+                               is_first_char = false
+                       else if char == '_' then
+                               follows_us = true
+                       else if follows_us then
+                               new_str.add(char.to_upper)
+                               follows_us = false
+                       else
+                               new_str.add(char)
+                       end
+               end
+
+               return new_str.to_s
+       end
+
+       # Returns a capitalized `self`
+       #
+       # Letters that follow a letter are lowercased
+       # Letters that follow a non-letter are upcased.
+       #
+       # SEE : `Char::is_letter` for the definition of letter.
+       #
+       #    assert "jAVASCRIPT".capitalized == "Javascript"
+       #    assert "i am root".capitalized == "I Am Root"
+       #    assert "ab_c -ab0c ab\nc".capitalized == "Ab_C -Ab0C Ab\nC"
+       fun capitalized: SELFTYPE do
+               if length == 0 then return self
+
+               var buf = new FlatBuffer.with_capacity(length)
+
+               var curr = chars[0].to_upper
+               var prev = curr
+               buf[0] = curr
+
+               for i in [1 .. length[ do
+                       prev = curr
+                       curr = self[i]
+                       if prev.is_letter then
+                               buf[i] = curr.to_lower
+                       else
+                               buf[i] = curr.to_upper
+                       end
+               end
+
+               return buf.to_s
+       end
+end
+
+private class FlatSubstringsIter
+       super Iterator[FlatText]
+
+       var tgt: nullable FlatText
+
+       redef fun item do
+               assert is_ok
+               return tgt.as(not null)
+       end
+
+       redef fun is_ok do return tgt != null
+
+       redef fun next do tgt = null
+end
 
-       redef type OTHER: String
+# Immutable strings of characters.
+class FlatString
+       super FlatText
+       super String
 
        # Index in _items of the start of the string
-       readable var _index_from: Int
+       private var index_from: Int is noinit
 
        # Indes in _items of the last item of the string
-       readable var _index_to: Int
+       private var index_to: Int is noinit
+
+       redef var chars: SequenceRead[Char] = new FlatStringCharView(self)
 
-       redef var chars: StringCharView = new FlatStringCharView(self)
+       redef fun [](index)
+       do
+               # Check that the index (+ index_from) is not larger than indexTo
+               # In other terms, if the index is valid
+               assert index >= 0
+               assert (index + index_from) <= index_to
+               return items[index + index_from]
+       end
 
        ################################################
        #       AbstractString specific methods        #
        ################################################
 
-       redef fun [](index) do
-               assert index >= 0
-               # Check that the index (+ index_from) is not larger than indexTo
-               # In other terms, if the index is valid
-               assert (index + _index_from) <= _index_to
-               return _items[index + _index_from]
+       redef fun reversed
+       do
+               var native = new NativeString(self.length + 1)
+               var length = self.length
+               var items = self.items
+               var pos = 0
+               var ipos = length-1
+               while pos < length do
+                       native[pos] = items[ipos]
+                       pos += 1
+                       ipos -= 1
+               end
+               return native.to_s_with_length(self.length)
        end
 
-       redef fun substring(from: Int, count: Int): String
+       redef fun substring(from, count)
        do
                assert count >= 0
 
@@ -436,56 +1020,27 @@ class String
                        from = 0
                end
 
-               var realFrom = _index_from + from
+               var realFrom = index_from + from
 
-               if (realFrom + count) > _index_to then return new String.with_infos(_items, _index_to - realFrom + 1, realFrom, _index_to)
+               if (realFrom + count) > index_to then return new FlatString.with_infos(items, index_to - realFrom + 1, realFrom, index_to)
 
-               if count == 0 then return ""
+               if count == 0 then return empty
 
                var to = realFrom + count - 1
 
-               return new String.with_infos(_items, to - realFrom + 1, realFrom, to)
-       end
-
-       redef fun substring_from(from: Int): String
-       do
-               if from > _length then return ""
-               if from < 0 then from = 0
-               return substring(from, _length)
+               return new FlatString.with_infos(items, to - realFrom + 1, realFrom, to)
        end
 
-       redef fun has_substring(str: String, pos: Int): Bool
-       do
-               var itsindex = str._length - 1
-
-               var myindex = pos + itsindex
-               var myitems = _items
-
-               var itsitems = str._items
-
-               if myindex > _length or itsindex > myindex then return false
-
-               var itsindexfrom = str.index_from
-               itsindex += itsindexfrom
-               myindex += index_from
-
-               while itsindex >= itsindexfrom do
-                       if myitems[myindex] != itsitems[itsindex] then return false
-                       myindex -= 1
-                       itsindex -= 1
-               end
-
-               return true
-       end
+       redef fun empty do return "".as(FlatString)
 
-       redef fun to_upper: String
+       redef fun to_upper
        do
-               var outstr = calloc_string(self._length + 1)
+               var outstr = new NativeString(self.length + 1)
                var out_index = 0
 
-               var myitems = self._items
-               var index_from = self._index_from
-               var max = self._index_to
+               var myitems = self.items
+               var index_from = self.index_from
+               var max = self.index_to
 
                while index_from <= max do
                        outstr[out_index] = myitems[index_from].to_upper
@@ -495,17 +1050,17 @@ class String
 
                outstr[self.length] = '\0'
 
-               return outstr.to_s_with_length(self._length)
+               return outstr.to_s_with_length(self.length)
        end
 
-       redef fun to_lower : String
+       redef fun to_lower
        do
-               var outstr = calloc_string(self._length + 1)
+               var outstr = new NativeString(self.length + 1)
                var out_index = 0
 
-               var myitems = self._items
-               var index_from = self._index_from
-               var max = self._index_to
+               var myitems = self.items
+               var index_from = self.index_from
+               var max = self.index_to
 
                while index_from <= max do
                        outstr[out_index] = myitems[index_from].to_lower
@@ -515,35 +1070,15 @@ class String
 
                outstr[self.length] = '\0'
 
-               return outstr.to_s_with_length(self._length)
-       end
-
-       redef fun trim: String
-       do
-               if self._length == 0 then return self
-               # find position of the first non white space char (ascii < 32) from the start of the string
-               var start_pos = self._index_from
-               while _items[start_pos].ascii <= 32 do
-                       start_pos += 1
-                       if start_pos == _index_to + 1 then return ""
-               end
-               # find position of the first non white space char from the end of the string
-               var end_pos = _index_to
-               while _items[end_pos].ascii <= 32 do
-                       end_pos -= 1
-                       if end_pos == start_pos then return _items[start_pos].to_s
-               end
-               start_pos -= index_from
-               end_pos -= index_from
-               return self.substring(start_pos, end_pos - start_pos + 1)
+               return outstr.to_s_with_length(self.length)
        end
 
        redef fun output
        do
-               var i = self._index_from
-               var imax = self._index_to
+               var i = self.index_from
+               var imax = self.index_to
                while i <= imax do
-                       _items[i].output
+                       items[i].output
                        i += 1
                end
        end
@@ -554,41 +1089,42 @@ class String
 
        private init with_infos(items: NativeString, len: Int, from: Int, to: Int)
        do
-               self._items = items
-               _length = len
-               _index_from = from
-               _index_to = to
+               self.items = items
+               length = len
+               index_from = from
+               index_to = to
        end
 
-       # Return a null terminated char *
-       fun to_cstring: NativeString
+       redef fun to_cstring: NativeString
        do
-               if _index_from > 0 or _index_to != items.cstring_length - 1 then
-                       var newItems = calloc_string(_length + 1)
-                       self.items.copy_to(newItems, _length, _index_from, 0)
+               if real_items != null then
+                       return real_items.as(not null)
+               else
+                       var newItems = new NativeString(length + 1)
+                       self.items.copy_to(newItems, length, index_from, 0)
                        newItems[length] = '\0'
+                       self.real_items = newItems
                        return newItems
                end
-               return _items
        end
 
        redef fun ==(other)
        do
-               if not other isa String then return false
+               if not other isa FlatString then return super
 
                if self.object_id == other.object_id then return true
 
-               var my_length = _length
+               var my_length = length
 
-               if other._length != my_length then return false
+               if other.length != my_length then return false
 
-               var my_index = _index_from
-               var its_index = other._index_from
+               var my_index = index_from
+               var its_index = other.index_from
 
                var last_iteration = my_index + my_length
 
-               var itsitems = other._items
-               var myitems = self._items
+               var itsitems = other.items
+               var myitems = self.items
 
                while my_index < last_iteration do
                        if myitems[my_index] != itsitems[its_index] then return false
@@ -599,24 +1135,23 @@ class String
                return true
        end
 
-       # The comparison between two strings is done on a lexicographical basis
-       #
-       #     assert ("aa" < "b")      ==  true
        redef fun <(other)
        do
+               if not other isa FlatString then return super
+
                if self.object_id == other.object_id then return false
 
                var my_curr_char : Char
                var its_curr_char : Char
 
-               var curr_id_self = self._index_from
-               var curr_id_other = other._index_from
+               var curr_id_self = self.index_from
+               var curr_id_other = other.index_from
 
-               var my_items = self._items
-               var its_items = other._items
+               var my_items = self.items
+               var its_items = other.items
 
-               var my_length = self._length
-               var its_length = other._length
+               var my_length = self.length
+               var its_length = other.length
 
                var max_iterations = curr_id_self + my_length
 
@@ -636,42 +1171,45 @@ class String
                return my_length < its_length
        end
 
-       # The concatenation of `self` with `s`
-       #
-       #     assert "hello " + "world!"         == "hello world!"
-       fun +(s: String): String
+       redef fun +(s)
        do
-               var my_length = self._length
-               var its_length = s._length
+               var my_length = self.length
+               var its_length = s.length
 
                var total_length = my_length + its_length
 
-               var target_string = calloc_string(my_length + its_length + 1)
+               var target_string = new NativeString(my_length + its_length + 1)
 
-               self._items.copy_to(target_string, my_length, _index_from, 0)
-               s._items.copy_to(target_string, its_length, s._index_from, my_length)
+               self.items.copy_to(target_string, my_length, index_from, 0)
+               if s isa FlatString then
+                       s.items.copy_to(target_string, its_length, s.index_from, my_length)
+               else if s isa FlatBuffer then
+                       s.items.copy_to(target_string, its_length, 0, my_length)
+               else
+                       var curr_pos = my_length
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               target_string[curr_pos] = c
+                               curr_pos += 1
+                       end
+               end
 
                target_string[total_length] = '\0'
 
                return target_string.to_s_with_length(total_length)
        end
 
-       # `i` repetitions of `self`
-       #
-       #     assert "abc"*3           == "abcabcabc"
-       #     assert "abc"*1           == "abc"
-       #     assert "abc"*0           == ""
-       fun *(i: Int): String
+       redef fun *(i)
        do
                assert i >= 0
 
-               var my_length = self._length
+               var my_length = self.length
 
                var final_length = my_length * i
 
-               var my_items = self._items
+               var my_items = self.items
 
-               var target_string = calloc_string((final_length) + 1)
+               var target_string = new NativeString(final_length + 1)
 
                target_string[final_length] = '\0'
 
@@ -685,38 +1223,65 @@ class String
                return target_string.to_s_with_length(final_length)
        end
 
-       redef fun to_s do return self
-
        redef fun hash
        do
-               # djb2 hash algorythm
-               var h = 5381
-               var i = _length - 1
+               if hash_cache == null then
+                       # djb2 hash algorithm
+                       var h = 5381
+                       var i = index_from
 
-               var myitems = _items
-               var strStart = _index_from
+                       var myitems = items
 
-               i += strStart
+                       while i <= index_to do
+                               h = h.lshift(5) + h + myitems[i].ascii
+                               i += 1
+                       end
 
-               while i >= strStart do
-                       h = (h * 32) + h + self._items[i].ascii
-                       i -= 1
+                       hash_cache = h
                end
 
-               return h
+               return hash_cache.as(not null)
+       end
+
+       redef fun substrings do return new FlatSubstringsIter(self)
+end
+
+private class FlatStringReverseIterator
+       super IndexedIterator[Char]
+
+       var target: FlatString
+
+       var target_items: NativeString
+
+       var curr_pos: Int
+
+       init with_pos(tgt: FlatString, pos: Int)
+       do
+               target = tgt
+               target_items = tgt.items
+               curr_pos = pos + tgt.index_from
        end
+
+       redef fun is_ok do return curr_pos >= target.index_from
+
+       redef fun item do return target_items[curr_pos]
+
+       redef fun next do curr_pos -= 1
+
+       redef fun index do return curr_pos - target.index_from
+
 end
 
 private class FlatStringIterator
        super IndexedIterator[Char]
 
-       var target: String
+       var target: FlatString
 
        var target_items: NativeString
 
        var curr_pos: Int
 
-       init with_pos(tgt: String, pos: Int)
+       init with_pos(tgt: FlatString, pos: Int)
        do
                target = tgt
                target_items = tgt.items
@@ -736,155 +1301,398 @@ end
 private class FlatStringCharView
        super StringCharView
 
-       redef type SELFTYPE: String
+       redef type SELFTYPE: FlatString
 
        redef fun [](index)
        do
                # Check that the index (+ index_from) is not larger than indexTo
                # In other terms, if the index is valid
                assert index >= 0
-               assert (index + target._index_from) <= target._index_to
-               return target._items[index + target._index_from]
+               var target = self.target
+               assert (index + target.index_from) <= target.index_to
+               return target.items[index + target.index_from]
+       end
+
+       redef fun iterator_from(start) do return new FlatStringIterator.with_pos(target, start)
+
+       redef fun reverse_iterator_from(start) do return new FlatStringReverseIterator.with_pos(target, start)
+
+end
+
+# A mutable sequence of characters.
+abstract class Buffer
+       super Text
+
+       redef type SELFTYPE: Buffer
+
+       # Specific implementations MUST set this to `true` in order to invalidate caches
+       protected var is_dirty = true
+
+       # Copy-On-Write flag
+       #
+       # If the `Buffer` was to_s'd, the next in-place altering
+       # operation will cause the current `Buffer` to be re-allocated.
+       #
+       # The flag will then be set at `false`.
+       protected var written = false
+
+       # Modifies the char contained at pos `index`
+       #
+       # DEPRECATED : Use self.chars.[]= instead
+       fun []=(index: Int, item: Char) is abstract
+
+       # Adds a char `c` at the end of self
+       #
+       # DEPRECATED : Use self.chars.add instead
+       fun add(c: Char) is abstract
+
+       # Clears the buffer
+       #
+       #     var b = new FlatBuffer
+       #     b.append "hello"
+       #     assert not b.is_empty
+       #     b.clear
+       #     assert b.is_empty
+       fun clear is abstract
+
+       # Enlarges the subsequent array containing the chars of self
+       fun enlarge(cap: Int) is abstract
+
+       # Adds the content of text `s` at the end of self
+       #
+       #     var b = new FlatBuffer
+       #     b.append "hello"
+       #     b.append "world"
+       #     assert b == "helloworld"
+       fun append(s: Text) is abstract
+
+       # `self` is appended in such a way that `self` is repeated `r` times
+       #
+       #     var b = new FlatBuffer
+       #     b.append "hello"
+       #     b.times 3
+       #     assert b == "hellohellohello"
+       fun times(r: Int) is abstract
+
+       # Reverses itself in-place
+       #
+       #     var b = new FlatBuffer
+       #     b.append("hello")
+       #     b.reverse
+       #     assert b == "olleh"
+       fun reverse is abstract
+
+       # Changes each lower-case char in `self` by its upper-case variant
+       #
+       #     var b = new FlatBuffer
+       #     b.append("Hello World!")
+       #     b.upper
+       #     assert b == "HELLO WORLD!"
+       fun upper is abstract
+
+       # Changes each upper-case char in `self` by its lower-case variant
+       #
+       #     var b = new FlatBuffer
+       #     b.append("Hello World!")
+       #     b.lower
+       #     assert b == "hello world!"
+       fun lower is abstract
+
+       # Capitalizes each word in `self`
+       #
+       # Letters that follow a letter are lowercased
+       # Letters that follow a non-letter are upcased.
+       #
+       # SEE: `Char::is_letter` for the definition of a letter.
+       #
+       #    var b = new FlatBuffer.from("jAVAsCriPt")
+       #    b.capitalize
+       #    assert b == "Javascript"
+       #    b = new FlatBuffer.from("i am root")
+       #    b.capitalize
+       #    assert b == "I Am Root"
+       #    b = new FlatBuffer.from("ab_c -ab0c ab\nc")
+       #    b.capitalize
+       #    assert b == "Ab_C -Ab0C Ab\nC"
+       fun capitalize do
+               if length == 0 then return
+               var c = self[0].to_upper
+               self[0] = c
+               var prev: Char = c
+               for i in [1 .. length[ do
+                       prev = c
+                       c = self[i]
+                       if prev.is_letter then
+                               self[i] = c.to_lower
+                       else
+                               self[i] = c.to_upper
+                       end
+               end
        end
 
-       redef fun iterator: IndexedIterator[Char] do return new FlatStringIterator.with_pos(target, 0)
+       redef fun hash
+       do
+               if is_dirty then hash_cache = null
+               return super
+       end
 
+       # In Buffers, the internal sequence of character is mutable
+       # Thus, `chars` can be used to modify the buffer.
+       redef fun chars: Sequence[Char] is abstract
 end
 
 # Mutable strings of characters.
-class Buffer
-       super AbstractString
-       super Comparable
-       super StringCapable
-       super AbstractArray[Char]
+class FlatBuffer
+       super FlatText
+       super Buffer
+
+       redef type SELFTYPE: FlatBuffer
+
+       redef var chars: Sequence[Char] = new FlatBufferCharView(self)
+
+       private var capacity: Int = 0
 
-       redef type OTHER: String
+       redef fun substrings do return new FlatSubstringsIter(self)
 
-       redef var chars: BufferCharView = new FlatBufferCharView(self)
+       # Re-copies the `NativeString` into a new one and sets it as the new `Buffer`
+       #
+       # This happens when an operation modifies the current `Buffer` and
+       # the Copy-On-Write flag `written` is set at true.
+       private fun reset do
+               var nns = new NativeString(capacity)
+               items.copy_to(nns, length, 0, 0)
+               items = nns
+               written = false
+       end
+
+       redef fun [](index)
+       do
+               assert index >= 0
+               assert index  < length
+               return items[index]
+       end
 
        redef fun []=(index, item)
        do
+               is_dirty = true
                if index == length then
                        add(item)
                        return
                end
+               if written then reset
                assert index >= 0 and index < length
-               _items[index] = item
+               items[index] = item
        end
 
        redef fun add(c)
        do
-               if _capacity <= length then enlarge(length + 5)
-               _items[length] = c
-               _length += 1
+               is_dirty = true
+               if capacity <= length then enlarge(length + 5)
+               items[length] = c
+               length += 1
+       end
+
+       redef fun clear do
+               is_dirty = true
+               if written then reset
+               length = 0
        end
 
+       redef fun empty do return new FlatBuffer
+
        redef fun enlarge(cap)
        do
-               var c = _capacity
+               var c = capacity
                if cap <= c then return
                while c <= cap do c = c * 2 + 2
-               var a = calloc_string(c+1)
-               _items.copy_to(a, length, 0, 0)
-               _items = a
-               _capacity = c
+               # The COW flag can be set at false here, since
+               # it does a copy of the current `Buffer`
+               written = false
+               var a = new NativeString(c+1)
+               if length > 0 then items.copy_to(a, length, 0, 0)
+               items = a
+               capacity = c
        end
 
-       redef fun append(s)
+       redef fun to_s: String
        do
-               if s isa String then
-                       var sl = s.length
-                       if _capacity < _length + sl then enlarge(_length + sl)
-                       s.items.copy_to(_items, sl, s._index_from, _length)
-                       _length += sl
+               written = true
+               if length == 0 then items = new NativeString(1)
+               return new FlatString.with_infos(items, length, 0, length - 1)
+       end
+
+       redef fun to_cstring
+       do
+               if is_dirty then
+                       var new_native = new NativeString(length + 1)
+                       new_native[length] = '\0'
+                       if length > 0 then items.copy_to(new_native, length, 0, 0)
+                       real_items = new_native
+                       is_dirty = false
+               end
+               return real_items.as(not null)
+       end
+
+       # Create a new empty string.
+       init do end
+
+       # Create a new string copied from `s`.
+       init from(s: Text)
+       do
+               capacity = s.length + 1
+               length = s.length
+               items = new NativeString(capacity)
+               if s isa FlatString then
+                       s.items.copy_to(items, length, s.index_from, 0)
+               else if s isa FlatBuffer then
+                       s.items.copy_to(items, length, 0, 0)
                else
-                       super
+                       var curr_pos = 0
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               items[curr_pos] = c
+                               curr_pos += 1
+                       end
                end
        end
 
-       redef fun to_s: String
+       # Create a new empty string with a given capacity.
+       init with_capacity(cap: Int)
        do
-               var l = length
-               var a = calloc_string(l+1)
-               _items.copy_to(a, l, 0, 0)
+               assert cap >= 0
+               # _items = new NativeString.calloc(cap)
+               items = new NativeString(cap+1)
+               capacity = cap
+               length = 0
+       end
 
-               # Ensure the afterlast byte is '\0' to nul-terminated char *
-               a[length] = '\0'
+       redef fun append(s)
+       do
+               if s.is_empty then return
+               is_dirty = true
+               var sl = s.length
+               if capacity < length + sl then enlarge(length + sl)
+               if s isa FlatString then
+                       s.items.copy_to(items, sl, s.index_from, length)
+               else if s isa FlatBuffer then
+                       s.items.copy_to(items, sl, 0, length)
+               else
+                       var curr_pos = self.length
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               items[curr_pos] = c
+                               curr_pos += 1
+                       end
+               end
+               length += sl
+       end
 
-               return a.to_s_with_length(length)
+       # Copies the content of self in `dest`
+       fun copy(start: Int, len: Int, dest: Buffer, new_start: Int)
+       do
+               var self_chars = self.chars
+               var dest_chars = dest.chars
+               for i in [0..len-1] do
+                       dest_chars[new_start+i] = self_chars[start+i]
+               end
        end
 
-       redef fun <(s)
+       redef fun substring(from, count)
        do
-               var i = 0
-               var l1 = length
-               var l2 = s.length
-               while i < l1 and i < l2 do
-                       var c1 = self.chars[i].ascii
-                       var c2 = s.chars[i].ascii
-                       if c1 < c2 then
-                               return true
-                       else if c2 < c1 then
-                               return false
+               assert count >= 0
+               count += from
+               if from < 0 then from = 0
+               if count > length then count = length
+               if from < count then
+                       var r = new FlatBuffer.with_capacity(count - from)
+                       while from < count do
+                               r.chars.push(items[from])
+                               from += 1
                        end
-                       i += 1
-               end
-               if l1 < l2 then
-                       return true
+                       return r
                else
-                       return false
+                       return new FlatBuffer
                end
        end
 
-       # Create a new empty string.
-       init
+       redef fun reverse
        do
-               with_capacity(5)
+               written = false
+               var ns = new NativeString(capacity)
+               var si = length - 1
+               var ni = 0
+               var it = items
+               while si >= 0 do
+                       ns[ni] = it[si]
+                       ni += 1
+                       si -= 1
+               end
+               items = ns
        end
 
-       init from(s: String)
+       redef fun times(repeats)
        do
-               _capacity = s.length + 1
-               _length = s.length
-               _items = calloc_string(_capacity)
-               s.items.copy_to(_items, _length, s._index_from, 0)
+               var x = new FlatString.with_infos(items, length, 0, length - 1)
+               for i in [1..repeats[ do
+                       append(x)
+               end
        end
 
-       # Create a new empty string with a given capacity.
-       init with_capacity(cap: Int)
+       redef fun upper
        do
-               assert cap >= 0
-               # _items = new NativeString.calloc(cap)
-               _items = calloc_string(cap+1)
-               _capacity = cap
-               _length = 0
+               if written then reset
+               var it = items
+               var id = length - 1
+               while id >= 0 do
+                       it[id] = it[id].to_upper
+                       id -= 1
+               end
        end
 
-       redef fun ==(o)
+       redef fun lower
        do
-               if not o isa Buffer then return false
-               var l = length
-               if o.length != l then return false
-               var i = 0
-               var it = _items
-               var oit = o._items
-               while i < l do
-                       if it[i] != oit[i] then return false
-                       i += 1
+               if written then reset
+               var it = items
+               var id = length - 1
+               while id >= 0 do
+                       it[id] = it[id].to_lower
+                       id -= 1
                end
-               return true
        end
+end
+
+private class FlatBufferReverseIterator
+       super IndexedIterator[Char]
+
+       var target: FlatBuffer
+
+       var target_items: NativeString
+
+       var curr_pos: Int
+
+       init with_pos(tgt: FlatBuffer, pos: Int)
+       do
+               target = tgt
+               if tgt.length > 0 then target_items = tgt.items
+               curr_pos = pos
+       end
+
+       redef fun index do return curr_pos
+
+       redef fun is_ok do return curr_pos >= 0
+
+       redef fun item do return target_items[curr_pos]
+
+       redef fun next do curr_pos -= 1
 
-       readable private var _capacity: Int
 end
 
 private class FlatBufferCharView
        super BufferCharView
-       super StringCapable
 
-       redef type SELFTYPE: Buffer
+       redef type SELFTYPE: FlatBuffer
 
-       redef fun [](index) do return target._items[index]
+       redef fun [](index) do return target.items[index]
 
        redef fun []=(index, item)
        do
@@ -893,7 +1701,7 @@ private class FlatBufferCharView
                        add(item)
                        return
                end
-               target._items[index] = item
+               target.items[index] = item
        end
 
        redef fun push(c)
@@ -913,28 +1721,29 @@ private class FlatBufferCharView
 
        redef fun append(s)
        do
-               var my_items = target.items
                var s_length = s.length
                if target.capacity < s.length then enlarge(s_length + target.length)
        end
 
-       redef fun iterator: IndexedIterator[Char] do return new FlatBufferIterator.with_pos(target, 0)
+       redef fun iterator_from(pos) do return new FlatBufferIterator.with_pos(target, pos)
+
+       redef fun reverse_iterator_from(pos) do return new FlatBufferReverseIterator.with_pos(target, pos)
 
 end
 
 private class FlatBufferIterator
        super IndexedIterator[Char]
 
-       var target: Buffer
+       var target: FlatBuffer
 
        var target_items: NativeString
 
        var curr_pos: Int
 
-       init with_pos(tgt: Buffer, pos: Int)
+       init with_pos(tgt: FlatBuffer, pos: Int)
        do
                target = tgt
-               target_items = tgt.items
+               if tgt.length > 0 then target_items = tgt.items
                curr_pos = pos
        end
 
@@ -977,11 +1786,6 @@ redef class Object
        do
                return "{class_name}:#{object_id.to_hex}"
        end
-
-       protected fun args: Sequence[String]
-       do
-               return sys.args
-       end
 end
 
 redef class Bool
@@ -998,9 +1802,18 @@ redef class Bool
 end
 
 redef class Int
+
+       # Wrapper of strerror C function
+       private fun strerror_ext: NativeString is extern `{
+               return strerror(recv);
+       `}
+
+       # Returns a string describing error number
+       fun strerror: String do return strerror_ext.to_s
+
        # Fill `s` with the digits in base `base` of `self` (and with the '-' sign if 'signed' and negative).
        # assume < to_c max const of char
-       fun fill_buffer(s: Buffer, base: Int, signed: Bool)
+       private fun fill_buffer(s: Buffer, base: Int, signed: Bool)
        do
                var n: Int
                # Sign
@@ -1023,32 +1836,39 @@ redef class Int
        end
 
        # C function to convert an nit Int to a NativeString (char*)
-       private fun native_int_to_s(len: Int): NativeString is extern "native_int_to_s"
+       private fun native_int_to_s: NativeString is extern "native_int_to_s"
 
        # return displayable int in base 10 and signed
        #
        #     assert 1.to_s            == "1"
        #     assert (-123).to_s       == "-123"
        redef fun to_s do
-               var len = digit_count(10)
-               return native_int_to_s(len).to_s_with_length(len)
+               return native_int_to_s.to_s
        end
 
-       # return displayable int in hexadecimal (unsigned (not now))
+       # return displayable int in hexadecimal
+       #
+       #     assert 1.to_hex  == "1"
+       #     assert (-255).to_hex  == "-ff"
        fun to_hex: String do return to_base(16,false)
 
        # return displayable int in base base and signed
        fun to_base(base: Int, signed: Bool): String
        do
                var l = digit_count(base)
-               var s = new Buffer.from(" " * l)
+               var s = new FlatBuffer.from(" " * l)
                fill_buffer(s, base, signed)
                return s.to_s
        end
 end
 
 redef class Float
-       # Pretty print self, print needoed decimals up to a max of 3.
+       # Pretty representation of `self`, with decimals as needed from 1 to a maximum of 3
+       #
+       #     assert 12.34.to_s       == "12.34"
+       #     assert (-0120.030).to_s == "-120.03"
+       #
+       # see `to_precision` for a custom precision.
        redef fun to_s do
                var str = to_precision( 3 )
                if is_inf != 0 or is_nan then return str
@@ -1067,8 +1887,15 @@ redef class Float
                return str
        end
 
-       # `self` representation with `nb` digits after the '.'.
-       fun to_precision(nb: Int): String
+       # `String` representation of `self` with the given number of `decimals`
+       #
+       #     assert 12.345.to_precision(0)    == "12"
+       #     assert 12.345.to_precision(3)    == "12.345"
+       #     assert (-12.345).to_precision(3) == "-12.345"
+       #     assert (-0.123).to_precision(3)  == "-0.123"
+       #     assert 0.999.to_precision(2)     == "1.00"
+       #     assert 0.999.to_precision(4)     == "0.9990"
+       fun to_precision(decimals: Int): String
        do
                if is_nan then return "nan"
 
@@ -1079,27 +1906,42 @@ redef class Float
                        return  "-inf"
                end
 
-               if nb == 0 then return self.to_i.to_s
+               if decimals == 0 then return self.to_i.to_s
                var f = self
-               for i in [0..nb[ do f = f * 10.0
+               for i in [0..decimals[ do f = f * 10.0
                if self > 0.0 then
                        f = f + 0.5
                else
                        f = f - 0.5
                end
                var i = f.to_i
-               if i == 0 then return "0.0"
-               var s = i.to_s
+               if i == 0 then return "0." + "0"*decimals
+
+               # Prepare both parts of the float, before and after the "."
+               var s = i.abs.to_s
                var sl = s.length
-               if sl > nb then
-                       var p1 = s.substring(0, s.length-nb)
-                       var p2 = s.substring(s.length-nb, nb)
-                       return p1 + "." + p2
+               var p1
+               var p2
+               if sl > decimals then
+                       # Has something before the "."
+                       p1 = s.substring(0, sl-decimals)
+                       p2 = s.substring(sl-decimals, decimals)
                else
-                       return "0." + ("0"*(nb-sl)) + s
+                       p1 = "0"
+                       p2 = "0"*(decimals-sl) + s
                end
+
+               if i < 0 then p1 = "-" + p1
+
+               return p1 + "." + p2
        end
 
+       # `self` representation with `nb` digits after the '.'.
+       #
+       #     assert 12.345.to_precision_native(1) == "12.3"
+       #     assert 12.345.to_precision_native(2) == "12.35"
+       #     assert 12.345.to_precision_native(3) == "12.345"
+       #     assert 12.345.to_precision_native(4) == "12.3450"
        fun to_precision_native(nb: Int): String import NativeString.to_s `{
                int size;
                char *str;
@@ -1116,33 +1958,43 @@ redef class Char
        #     assert 'x'.to_s    == "x"
        redef fun to_s
        do
-               var s = new Buffer.with_capacity(1)
+               var s = new FlatBuffer.with_capacity(1)
                s.chars[0] = self
                return s.to_s
        end
 
        # Returns true if the char is a numerical digit
+       #
+       #      assert '0'.is_numeric
+       #      assert '9'.is_numeric
+       #      assert not 'a'.is_numeric
+       #      assert not '?'.is_numeric
        fun is_numeric: Bool
        do
-               if self >= '0' and self <= '9'
-               then
-                       return true
-               end
-               return false
+               return self >= '0' and self <= '9'
        end
 
        # Returns true if the char is an alpha digit
+       #
+       #      assert 'a'.is_alpha
+       #      assert 'Z'.is_alpha
+       #      assert not '0'.is_alpha
+       #      assert not '?'.is_alpha
        fun is_alpha: Bool
        do
-               if (self >= 'a' and self <= 'z') or (self >= 'A' and self <= 'Z') then return true
-               return false
+               return (self >= 'a' and self <= 'z') or (self >= 'A' and self <= 'Z')
        end
 
        # Returns true if the char is an alpha or a numeric digit
+       #
+       #      assert 'a'.is_alphanumeric
+       #      assert 'Z'.is_alphanumeric
+       #      assert '0'.is_alphanumeric
+       #      assert '9'.is_alphanumeric
+       #      assert not '?'.is_alphanumeric
        fun is_alphanumeric: Bool
        do
-               if self.is_numeric or self.is_alpha then return true
-               return false
+               return self.is_numeric or self.is_alpha
        end
 end
 
@@ -1150,7 +2002,7 @@ redef class Collection[E]
        # Concatenate elements.
        redef fun to_s
        do
-               var s = new Buffer
+               var s = new FlatBuffer
                for e in self do if e != null then s.append(e.to_s)
                return s.to_s
        end
@@ -1159,11 +2011,11 @@ redef class Collection[E]
        #
        #     assert [1, 2, 3].join(":")         == "1:2:3"
        #     assert [1..3].join(":")            == "1:2:3"
-       fun join(sep: String): String
+       fun join(sep: Text): String
        do
                if is_empty then return ""
 
-               var s = new Buffer # Result
+               var s = new FlatBuffer # Result
 
                # Concat first item
                var i = iterator
@@ -1183,18 +2035,51 @@ redef class Collection[E]
 end
 
 redef class Array[E]
+
        # Fast implementation
        redef fun to_s
        do
-               var s = new Buffer
-               var i = 0
                var l = length
+               if l == 0 then return ""
+               if l == 1 then if self[0] == null then return "" else return self[0].to_s
+               var its = _items
+               var na = new NativeArray[String](l)
+               var i = 0
+               var sl = 0
+               var mypos = 0
                while i < l do
-                       var e = self[i]
-                       if e != null then s.append(e.to_s)
+                       var itsi = its[i]
+                       if itsi == null then
+                               i += 1
+                               continue
+                       end
+                       var tmp = itsi.to_s
+                       sl += tmp.length
+                       na[mypos] = tmp
                        i += 1
+                       mypos += 1
                end
-               return s.to_s
+               var ns = new NativeString(sl + 1)
+               ns[sl] = '\0'
+               i = 0
+               var off = 0
+               while i < mypos do
+                       var tmp = na[i]
+                       var tpl = tmp.length
+                       if tmp isa FlatString then
+                               tmp.items.copy_to(ns, tpl, tmp.index_from, off)
+                               off += tpl
+                       else
+                               for j in tmp.substrings do
+                                       var s = j.as(FlatString)
+                                       var slen = s.length
+                                       s.items.copy_to(ns, slen, s.index_from, off)
+                                       off += slen
+                               end
+                       end
+                       i += 1
+               end
+               return ns.to_s_with_length(sl)
        end
 end
 
@@ -1211,7 +2096,7 @@ redef class Map[K,V]
        do
                if is_empty then return ""
 
-               var s = new Buffer # Result
+               var s = new FlatBuffer # Result
 
                # Concat first item
                var i = iterator
@@ -1237,11 +2122,17 @@ end
 ###############################################################################
 
 # Native strings are simple C char *
-class NativeString
-       super StringCapable
+extern class NativeString `{ char* `}
+       # Creates a new NativeString with a capacity of `length`
+       new(length: Int) is intern
 
+       # Get char at `index`.
        fun [](index: Int): Char is intern
+
+       # Set char `item` at index.
        fun []=(index: Int, item: Char) is intern
+
+       # Copy `self` to `dest`.
        fun copy_to(dest: NativeString, length: Int, from: Int, to: Int) is intern
 
        # Position of the first nul character.
@@ -1251,7 +2142,11 @@ class NativeString
                while self[l] != '\0' do l += 1
                return l
        end
+
+       # Parse `self` as an Int.
        fun atoi: Int is intern
+
+       # Parse `self` as a Float.
        fun atof: Float is extern "atof"
 
        redef fun to_s
@@ -1259,31 +2154,32 @@ class NativeString
                return to_s_with_length(cstring_length)
        end
 
-       fun to_s_with_length(length: Int): String
+       # Returns `self` as a String of `length`.
+       fun to_s_with_length(length: Int): FlatString
        do
                assert length >= 0
-               return new String.with_infos(self, length, 0, length - 1)
+               var str = new FlatString.with_infos(self, length, 0, length - 1)
+               return str
        end
 
-       fun to_s_with_copy: String
+       # Returns `self` as a new String.
+       fun to_s_with_copy: FlatString
        do
                var length = cstring_length
-               var new_self = calloc_string(length + 1)
+               var new_self = new NativeString(length + 1)
                copy_to(new_self, length, 0, 0)
-               return new String.with_infos(new_self, length, 0, length - 1)
+               var str = new FlatString.with_infos(new_self, length, 0, length - 1)
+               new_self[length] = '\0'
+               str.real_items = new_self
+               return str
        end
-
-end
-
-# StringCapable objects can create native strings
-interface StringCapable
-       protected fun calloc_string(size: Int): NativeString is intern
 end
 
 redef class Sys
-       var _args_cache: nullable Sequence[String]
+       private var args_cache: nullable Sequence[String]
 
-       redef fun args: Sequence[String]
+       # The arguments of the program as given by the OS
+       fun program_args: Sequence[String]
        do
                if _args_cache == null then init_args
                return _args_cache.as(not null)
@@ -1295,7 +2191,7 @@ redef class Sys
                return native_argv(0).to_s
        end
 
-       # Initialize `args` with the contents of `native_argc` and `native_argv`.
+       # Initialize `program_args` with the contents of `native_argc` and `native_argv`.
        private fun init_args
        do
                var argc = native_argc
@@ -1328,7 +2224,8 @@ end
 #
 # Note: it caching is not usefull, see `alpha_comparator`
 class CachedAlphaComparator
-       super AbstractSorter[Object]
+       super Comparator
+       redef type COMPARED: Object
 
        private var cache = new HashMap[Object, String]
 
@@ -1346,7 +2243,7 @@ end
 
 # see `alpha_comparator`
 private class AlphaComparator
-       super AbstractSorter[Object]
+       super Comparator
        redef fun compare(a, b) do return a.to_s <=> b.to_s
 end
 
@@ -1358,4 +2255,10 @@ end
 #     var a = [1, 2, 3, 10, 20]
 #     alpha_comparator.sort(a)
 #     assert a == [1, 10, 2, 20, 3]
-fun alpha_comparator: AbstractSorter[Object] do return once new AlphaComparator
+fun alpha_comparator: Comparator do return once new AlphaComparator
+
+# The arguments of the program as given by the OS
+fun args: Sequence[String]
+do
+       return sys.program_args
+end