lib/standard/string: SELFTYPE now refers to String instead of its implementations.
[nit.git] / lib / standard / string.nit
index d1c4b7c..13bf585 100644 (file)
 #
 # This file is free software, which comes along with NIT.  This software is
 # distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
-# without  even  the implied warranty of  MERCHANTABILITY or  FITNESS FOR A 
+# without  even  the implied warranty of  MERCHANTABILITY or  FITNESS FOR A
 # PARTICULAR PURPOSE.  You can modify it is you want,  provided this header
 # is kept unaltered, and a notification of the changes is added.
 # You  are  allowed  to  redistribute it and sell it, alone or is a part of
 # another product.
 
 # Basic manipulations of strings of characters
-package string
+module string
 
+import math
 intrude import collection # FIXME should be collection::array
-import hash
+
+`{
+#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
+       super StringCapable
+
+       redef type OTHER: Text
 
-       readable private var _items: NativeString
+       # Type of self (used for factorization of several methods, ex : substring_from, empty...)
+       type SELFTYPE: Text
 
-       redef fun [](index) do return _items[index]
+       # Gets a view on the chars of the Text object
+       #
+       #     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.
        #
-       # "abcd".substring(1, 2)        # --> "bc"
-       # "abcd".substring(-1, 2)       # --> "a"
-       # "abcd".substring(1, 0)     # --> ""
-       # "abcd".substring(2, 5)     # --> "cd"
-       fun substring(from: Int, count: Int): String
+       #     assert "abcd".substring(1, 2)      ==  "bc"
+       #     assert "abcd".substring(-1, 2)     ==  "a"
+       #     assert "abcd".substring(1, 0)      ==  ""
+       #     assert "abcd".substring(2, 5)      ==  "cd"
+       #
+       # 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): SELFTYPE is abstract
+
+       # Iterates on the substrings of self if any
+       fun substrings: Iterator[Text] is abstract
+
+       # Concatenates `o` to `self`
+       #
+       #     assert "hello" + "world"  == "helloworld"
+       #     assert "" + "hello" + ""  == "hello"
+       fun +(o: Text): SELFTYPE is abstract
+
+       # Auto-concatenates self `i` times
+       #
+       #     assert "abc" * 4 == "abcabcabcabc"
+       #     assert "abc" * 1 == "abc"
+       #     assert "abc" * 0 == ""
+       fun *(i: Int): SELFTYPE 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.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
 
-       # Create a substring from `self' beginning at the 'from' position
+       # Gets the last index of char ´c´
        #
-       # "abcd".substring(1)   # --> "bcd"
-       # "abcd".substring(-1)  # --> "abcd"
-       # "abcd".substring(2)     # --> "cd"
-       fun substring_from(from: Int): String
+       # Returns -1 if not found
+       #
+       # DEPRECATED : Use self.chars.last_index_of instead
+       fun last_index_of(c: Char): Int
        do
-               assert from < length
+               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
+
+       # Is 'c' contained in self ?
+       #
+       # DEPRECATED : Use self.chars.has instead
+       fun has(c: Char): Bool
+       do
+               return self.chars.has(c)
+       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"
+       #     assert "abcd".substring_from(-1)   ==  "abcd"
+       #     assert "abcd".substring_from(2)    ==  "cd"
+       #
+       # As with substring, a `from` index < 0 will be replaced by 0
+       fun substring_from(from: Int): SELFTYPE
+       do
+               if from > self.length then return empty
+               if from < 0 then from = 0
                return substring(from, length - from)
        end
 
-       # Does self have a substring 'str' starting from position 'pos
+       # Returns a reversed version of self
+       #
+       #     assert "hello".reversed  == "olleh"
+       #     assert "bob".reversed    == "bob"
+       #     assert "".reversed       == ""
+       fun reversed: SELFTYPE is abstract
+
+       # Does self have a substring `str` starting from position `pos`?
        #
-       # "abcd".has_substring("bc",1)  # --> true
-       # "abcd".has_substring("bc",2)  # --> false
+       #     assert "abcd".has_substring("bc",1)            ==  true
+       #     assert "abcd".has_substring("bc",2)            ==  false
        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._indexFrom
-               itsindex += its_index_from
-               while itsindex >= its_index_from do
-                       if myitems[myindex] != itsitems[itsindex] then return false
-                       myindex -= 1
-                       itsindex -= 1
+               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
 
-       # Is this string prefixed by 'prefix'
+       # Is this string prefixed by `prefix`?
        #
-       # "abc".is_prefix("abcd")       # --> true
-       # "bc".is_prefix("abcd")        # --> false
+       #     assert "abcd".has_prefix("ab")           ==  true
+       #     assert "abcbc".has_prefix("bc")          ==  false
+       #     assert "ab".has_prefix("abcd")           ==  false
        fun has_prefix(prefix: String): Bool do return has_substring(prefix,0)
 
-       # Is this string suffixed by 'suffix'
+       # Is this string suffixed by `suffix`?
        #
-       # "abcd".has_suffix("abc")      # --> false
-       # "abcd".has_suffix("bcd")      # --> true
+       #     assert "abcd".has_suffix("abc")        ==  false
+       #     assert "abcd".has_suffix("bcd")        ==  true
        fun has_suffix(suffix: String): Bool do return has_substring(suffix, length - suffix.length)
 
-       # If `self' contains only digits, return the corresponding integer
+       # If `self` contains only digits, return the corresponding integer
+       #
+       #     assert "123".to_i        == 123
+       #     assert "-1".to_i         == -1
        fun to_i: Int
        do
                # Shortcut
                return to_s.to_cstring.atoi
        end
 
-       # If `self' contains a float, return the corresponding float
+       # If `self` contains a float, return the corresponding float
+       #
+       #     assert "123".to_f        == 123.0
+       #     assert "-1".to_f         == -1.0
+       #     assert "-1.2e-3".to_f    == -0.0012
        fun to_f: Float
        do
                # Shortcut
                return to_s.to_cstring.atof
        end
 
-       # If `self' contains only digits and alpha <= 'f', return the corresponding integer.
+       # 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
+       # If `self` contains only digits and letters, return the corresponding integer in a given base
+       #
+       #     assert "120".a_to(3)     == 15
        fun a_to(base: Int) : Int
        do
                var i = 0
                var neg = false
 
-               for c in self
+               for c in self.chars
                do
                        var v = c.to_i
                        if v > base then
@@ -142,11 +289,16 @@ abstract class AbstractString
                end
        end
 
-       # Returns true if the string contains only Numeric values (and one "," or one "." character)
+       # Returns `true` if the string contains only Numeric values (and one "," or one "." character)
+       #
+       #     assert "123".is_numeric  == true
+       #     assert "1.2".is_numeric  == true
+       #     assert "1,2".is_numeric  == true
+       #     assert "1..2".is_numeric == false
        fun is_numeric: Bool
        do
                var has_point_or_comma = false
-               for i in self
+               for i in self.chars
                do
                        if not i.is_numeric
                        then
@@ -161,63 +313,356 @@ abstract class AbstractString
                return true
        end
 
-       # A upper case version of `self'
-       fun to_upper: String
+       # 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
+
+       # 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 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'
-       fun to_lower : String
+       # Removes the whitespaces at the end of self
+       #
+       #     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 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 == length then return self.empty
+               return self.substring(0, iter.index + 1)
+       end
+
+       # Trims trailing and preceding white spaces
+       # A whitespace is defined as any character which ascii value is less than or equal to 32
+       #
+       #     assert "  Hello  World !  ".trim   == "Hello  World !"
+       #     assert "\na\nb\tc\t".trim          == "a\nb\tc"
+       fun trim: SELFTYPE do return (self.l_trim).r_trim
+
+       # Mangle a string to be a unique string only made of alphanumeric characters
+       fun to_cmangle: String
+       do
+               var res = new FlatBuffer
+               var underscore = false
+               for c in self.chars do
+                       if (c >= 'a' and c <= 'z') or (c >='A' and c <= 'Z') then
+                               res.add(c)
+                               underscore = false
+                               continue
+                       end
+                       if underscore then
+                               res.append('_'.ascii.to_s)
+                               res.add('d')
+                       end
+                       if c >= '0' and c <= '9' then
+                               res.add(c)
+                               underscore = false
+                       else if c == '_' then
+                               res.add(c)
+                               underscore = true
+                       else
+                               res.add('_')
+                               res.append(c.ascii.to_s)
+                               res.add('d')
+                               underscore = false
+                       end
+               end
+               return res.to_s
+       end
+
+       # Escape " \ ' and non printable characters using the rules of literal C strings and characters
+       #
+       #     assert "abAB12<>&".escape_to_c         == "abAB12<>&"
+       #     assert "\n\"'\\".escape_to_c         == "\\n\\\"\\'\\\\"
+       fun escape_to_c: String
+       do
+               var b = new FlatBuffer
+               for c in self.chars do
+                       if c == '\n' then
+                               b.append("\\n")
+                       else if c == '\0' then
+                               b.append("\\0")
+                       else if c == '"' then
+                               b.append("\\\"")
+                       else if c == '\'' then
+                               b.append("\\\'")
+                       else if c == '\\' then
+                               b.append("\\\\")
+                       else if c.ascii < 32 then
+                               b.append("\\{c.ascii.to_base(8, false)}")
+                       else
+                               b.add(c)
+                       end
+               end
+               return b.to_s
+       end
+
+       # Escape additionnal characters
+       # The result might no be legal in C but be used in other languages
+       #
+       #     assert "ab|\{\}".escape_more_to_c("|\{\}") == "ab\\|\\\{\\\}"
+       fun escape_more_to_c(chars: String): String
+       do
+               var b = new FlatBuffer
+               for c in escape_to_c.chars do
+                       if chars.chars.has(c) then
+                               b.add('\\')
+                       end
+                       b.add(c)
+               end
+               return b.to_s
+       end
+
+       # Escape to C plus braces
+       #
+       #     assert "\n\"'\\\{\}".escape_to_nit      == "\\n\\\"\\'\\\\\\\{\\\}"
+       fun escape_to_nit: String do return escape_more_to_c("\{\}")
+
+       # Return a string where Nit escape sequences are transformed.
+       #
+       #     var s = "\\n"
+       #     assert s.length        ==  2
+       #     var u = s.unescape_nit
+       #     assert u.length        ==  1
+       #     assert u.chars[0].ascii      ==  10 # (the ASCII value of the "new line" character)
+       fun unescape_nit: String
+       do
+               var res = new FlatBuffer.with_capacity(self.length)
+               var was_slash = false
+               for c in chars do
+                       if not was_slash then
+                               if c == '\\' then
+                                       was_slash = true
+                               else
+                                       res.add(c)
+                               end
+                               continue
+                       end
+                       was_slash = false
+                       if c == 'n' then
+                               res.add('\n')
+                       else if c == 'r' then
+                               res.add('\r')
+                       else if c == 't' then
+                               res.add('\t')
+                       else if c == '0' then
+                               res.add('\0')
+                       else
+                               res.add(c)
+                       end
+               end
+               return res.to_s
        end
 
+       # 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
+               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
+
+       # Lexicographical comparaison
+       #
+       #     assert "abc" < "xy"
+       #     assert "ABC" < "abc"
+       redef fun <(other)
+       do
+               var self_chars = self.chars.iterator
+               var other_chars = other.chars.iterator
+
+               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
+
+       # Flat representation of self
+       fun flatten: FlatText is abstract
+
+       private var hash_cache: nullable Int = null
+
+       redef fun hash
+       do
+               if hash_cache == null then
+                       # djb2 hash algorithm
+                       var h = 5381
+
+                       for char in self.chars do
+                               h = h.lshift(5) + h + char.ascii
+                       end
+
+                       hash_cache = h
+               end
+               return hash_cache.as(not null)
+       end
+
+end
+
+# All kinds of array-based text representations.
+abstract class FlatText
+       super Text
+
+       private var items: NativeString
+
+       # Real items, used as cache for to_cstring is called
+       private var real_items: nullable NativeString = null
+
+       redef var length: Int = 0
+
+       init do end
 
        redef fun output
        do
                var i = 0
                while i < length do
-                       _items[i].output
+                       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
+
+       private var target: SELFTYPE
+
+       private init(tgt: SELFTYPE)
+       do
+               target = tgt
+       end
+
+       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
+private abstract class BufferCharView
+       super StringCharView
+       super Sequence[Char]
+
+       redef type SELFTYPE: Buffer
+
+end
+
+abstract class String
+       super Text
+
+       redef type SELFTYPE: String
+
+       redef fun to_s do return self
+end
+
+private class FlatSubstringsIter
+       super Iterator[FlatText]
+
+       var tgt: nullable FlatText
+
+       init(tgt: FlatText) do self.tgt = tgt
+
+       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
 
 # Immutable strings of characters.
-class String
-       super Comparable
-       super AbstractString
-       super StringCapable
+class FlatString
+       super FlatText
+       super String
+
+       # Index in _items of the start of the string
+       private var index_from: Int
 
-       redef type OTHER: String
+       # Indes in _items of the last item of the string
+       private var index_to: Int
 
-       readable var _indexFrom: Int
-       readable var _indexTo: Int
+       redef var chars: SequenceRead[Char] = new FlatStringCharView(self)
 
        ################################################
        #       AbstractString specific methods        #
        ################################################
 
-       # Access a character at index in String
-       #
-       redef fun [](index) do
-               assert index >= 0
-               assert (index + _indexFrom) < (_indexFrom + _length)
-               return items[index + _indexFrom]
+       redef fun reversed
+       do
+               var native = calloc_string(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
 
-       # Create a substring.
-       #
-       # "abcd".substring(1, 2)        # --> "bc"
-       # "abcd".substring(-1, 2)       # --> "a"
-       # "abcd".substring(1, 0)     # --> ""
-       # "abcd".substring(2, 5)     # --> "cd"
-       redef fun substring(from: Int, count: Int): String
+       redef fun substring(from, count)
        do
                assert count >= 0
 
@@ -227,102 +672,65 @@ class String
                        from = 0
                end
 
-               var realFrom = _indexFrom + from
+               var realFrom = index_from + from
 
-               if (realFrom + count) > _indexTo then return new String.from_substring(realFrom, _indexTo, _items)
+               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
 
-               return new String.from_substring(realFrom, realFrom + count - 1, _items)
-       end
+               var to = realFrom + count - 1
 
-       # Create a substring from `self' beginning at the 'from' position
-       #
-       # "abcd".substring(1)   # --> "bcd"
-       # "abcd".substring(-1)  # --> "abcd"
-       # "abcd".substring(2)     # --> "cd"
-       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
 
-       # Does self have a substring 'str' starting from position 'pos
-       #
-       # "abcd".has_substring("bc",1)  # --> true
-       # "abcd".has_substring("bc",2)  # --> false
-       redef fun has_substring(str: String, pos: Int): Bool
-       do
-               var itsindex = str._length - 1
+       redef fun empty do return "".as(FlatString)
 
-               var myindex = pos + itsindex
-               var myitems = _items
-
-               var itsitems = str._items
-
-               if myindex > _length or itsindex > myindex then return false
-
-               var itsindexfrom = str.indexFrom
-               itsindex += itsindexfrom
-               myindex += indexFrom
-
-               while itsindex >= itsindexfrom do
-                       if myitems[myindex] != itsitems[itsindex] then return false
-                       myindex -= 1
-                       itsindex -= 1
-               end
-
-               return true
-       end
-
-       # A upper case version of `self'
-       redef fun to_upper: String
+       redef fun to_upper
        do
-               var outstr = calloc_string(self._length + 1)
-               var index = 0
+               var outstr = calloc_string(self.length + 1)
+               var out_index = 0
 
-               var myitems = self._items
-               var index_from = self._indexFrom
-               var max = self._indexTo
+               var myitems = self.items
+               var index_from = self.index_from
+               var max = self.index_to
 
                while index_from <= max do
-                       outstr[index] = myitems[index_from].to_upper
-                       index += 1
+                       outstr[out_index] = myitems[index_from].to_upper
+                       out_index += 1
                        index_from += 1
                end
 
                outstr[self.length] = '\0'
 
-               return new String.with_native(outstr, self._length)
+               return outstr.to_s_with_length(self.length)
        end
 
-       # A lower case version of `self'
-       redef fun to_lower : String
+       redef fun to_lower
        do
-               var outstr = calloc_string(self._length + 1)
-               var index = 0
+               var outstr = calloc_string(self.length + 1)
+               var out_index = 0
 
-               var myitems = self._items
-               var index_from = self._indexFrom
-               var max = self._indexTo
+               var myitems = self.items
+               var index_from = self.index_from
+               var max = self.index_to
 
                while index_from <= max do
-                       outstr[index] = myitems[index_from].to_lower
-                       index += 1
+                       outstr[out_index] = myitems[index_from].to_lower
+                       out_index += 1
                        index_from += 1
                end
 
                outstr[self.length] = '\0'
 
-               return new String.with_native(outstr, self._length)
+               return outstr.to_s_with_length(self.length)
        end
 
        redef fun output
        do
-               var i = self._indexFrom
-               while i < length do
-                       _items[i].output
+               var i = self.index_from
+               var imax = self.index_to
+               while i <= imax do
+                       items[i].output
                        i += 1
                end
        end
@@ -331,280 +739,575 @@ class String
        #              String Specific Methods           #
        ##################################################
 
-       # Creates a String object as a substring of another String
-       private init from_substring(from: Int, to: Int, internalString: NativeString)
-       do
-               _items = internalString
-               _indexFrom = from
-               _indexTo = to
-               _length = to - from + 1
-       end
-
-       # Create a new string from a given char *.
-       init with_native(nat: NativeString, size: Int)
+       private init with_infos(items: NativeString, len: Int, from: Int, to: Int)
        do
-               assert size >= 0
-               _items = nat
-               _length = size
-               _indexFrom = 0
-               _indexTo = size - 1
+               self.items = items
+               length = len
+               index_from = from
+               index_to = to
        end
 
-       # Create a new string from a null terminated char *.
-       init from_cstring(str: NativeString)
+       redef fun to_cstring: NativeString
        do
-               with_native(str,str.cstring_length)
-       end
-
-       # Return a null terminated char *
-       fun to_cstring: NativeString
-       do
-               #return items
-               if _indexFrom > 0 or _indexTo != items.cstring_length-1 then
-                       var newItems = calloc_string(length+1)
-                       self.items.copy_to(newItems, _length, _indexFrom, 0)
+               if real_items != null then return real_items.as(not null)
+               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)
                        newItems[length] = '\0'
+                       self.real_items = newItems
                        return newItems
                end
-               return _items
+               return items
        end
 
-       redef fun ==(o)
+       redef fun ==(other)
        do
-               if not o isa String or o is null then return false
+               if not other isa FlatString then return super
 
-               if self.object_id == o.object_id then return true
+               if self.object_id == other.object_id then return true
 
-               var l = _length
+               var my_length = length
 
-               if o._length != l then return false
+               if other.length != my_length then return false
 
-               var i = _indexFrom
-               var j = o._indexFrom
-               var max = l + _indexFrom
-               var itsitems = o._items
-               var myitems = self._items
+               var my_index = index_from
+               var its_index = other.index_from
 
-               while i < max do
-                       if myitems[i] != itsitems[j] then return false
-                       i += 1
-                       j += 1
+               var last_iteration = my_index + my_length
+
+               var itsitems = other.items
+               var myitems = self.items
+
+               while my_index < last_iteration do
+                       if myitems[my_index] != itsitems[its_index] then return false
+                       my_index += 1
+                       its_index += 1
                end
 
                return true
        end
 
-       redef fun <(s)
+       redef fun <(other)
        do
-               if self.object_id == s.object_id then return false
+               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 c1 : Int
-               var c2 : Int
-               var currIdSelf = self._indexFrom
-               var currIdOther = s._indexFrom
-               var my_items = self._items
-               var its_items = s._items
+               var my_items = self.items
+               var its_items = other.items
 
-               var self_upper_bound = self._length + currIdSelf
-               var other_upper_bound = s._length + currIdOther
+               var my_length = self.length
+               var its_length = other.length
 
-               while currIdSelf < self_upper_bound and currIdOther < other_upper_bound do
-                       c1 = my_items[currIdSelf].ascii
-                       c2 = its_items[currIdOther].ascii
+               var max_iterations = curr_id_self + my_length
 
-                       if c1 < c2 then
-                               return true
-                       else if c2 < c1 then
+               while curr_id_self < max_iterations do
+                       my_curr_char = my_items[curr_id_self]
+                       its_curr_char = its_items[curr_id_other]
+
+                       if my_curr_char != its_curr_char then
+                               if my_curr_char < its_curr_char then return true
                                return false
                        end
 
-                       currIdSelf += 1
-                       currIdOther += 1
+                       curr_id_self += 1
+                       curr_id_other += 1
                end
 
-               if self._length < s._length then
-                       return true
-               else
-                       return false
-               end
+               return my_length < its_length
        end
 
-       # The concatenation of `self' with `r'
-       fun +(s: String): String
+       redef fun +(s)
        do
-               var newString = calloc_string(_length + s._length + 1)
+               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)
 
-               self._items.copy_to(newString, _length, _indexFrom, 0)
-               s._items.copy_to(newString, s._length, s._indexFrom, _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 s.chars do
+                               target_string[curr_pos] = i
+                               curr_pos += 1
+                       end
+               end
 
-               newString[self._length + s._length] = '\0'
+               target_string[total_length] = '\0'
 
-               return new String.with_native(newString, _length + s._length)
+               return target_string.to_s_with_length(total_length)
        end
 
-       # i repetitions of self
-       fun *(i: Int): String
+       redef fun *(i)
        do
                assert i >= 0
-               var r = calloc_string((_length * i) + 1)
 
-               r[_length * i] = '\0'
+               var my_length = self.length
+
+               var final_length = my_length * i
 
-               var lastStr = new String.with_native(r, (_length * i))
+               var my_items = self.items
 
-               while i > 0 do
-                       self._items.copy_to(r, _length, _indexFrom, _length*(i-1))
-                       i -= 1
+               var target_string = calloc_string((final_length) + 1)
+
+               target_string[final_length] = '\0'
+
+               var current_last = 0
+
+               for iteration in [1 .. i] do
+                       my_items.copy_to(target_string, my_length, 0, current_last)
+                       current_last += my_length
                end
 
-               return lastStr
+               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 = self.items
-               var index_from = self._indexFrom
+                       var myitems = items
 
-               i += index_from
+                       while i <= index_to do
+                               h = h.lshift(5) + h + myitems[i].ascii
+                               i += 1
+                       end
 
-               while i >= index_from 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 >= 0
+
+       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: 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 + target.index_from
+       end
+
+       redef fun is_ok do return curr_pos <= target.index_to
+
+       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 FlatStringCharView
+       super StringCharView
+
+       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
+               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
+
+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
+
+       # 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
+
+       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)
 
-       redef type OTHER: String
+       private var capacity: Int = 0
+
+       redef fun substrings do return new FlatSubstringsIter(self)
 
        redef fun []=(index, item)
        do
+               is_dirty = true
                if index == length then
                        add(item)
                        return
                end
                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
+               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
+               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
+               return to_cstring.to_s_with_length(length)
+       end
+
+       redef fun to_cstring
+       do
+               if is_dirty then
+                       var new_native = calloc_string(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
+
+       init from(s: Text)
        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._indexFrom, _length)
-                       _length += sl
+               capacity = s.length + 1
+               length = s.length
+               items = calloc_string(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 s.chars do
+                               items[curr_pos] = i
+                               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 = calloc_string(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 s.chars do
+                               items[curr_pos] = i
+                               curr_pos += 1
+                       end
+               end
+               length += sl
+       end
 
-               return new String.with_native(a, 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[i].ascii
-                       var c2 = s[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 reversed
        do
-               with_capacity(5)
+               var new_buf = new FlatBuffer.with_capacity(self.length)
+               var reviter = self.chars.reverse_iterator
+               while reviter.is_ok do
+                       new_buf.add(reviter.item)
+                       reviter.next
+               end
+               return new_buf
        end
 
-       init from(s: String)
+       redef fun +(other)
        do
-               _capacity = s.length + 1
-               _length = s.length
-               _items = calloc_string(_capacity)
-               s.items.copy_to(_items, _length, s._indexFrom, 0)
+               var new_buf = new FlatBuffer.with_capacity(self.length + other.length)
+               new_buf.append(self)
+               new_buf.append(other)
+               return new_buf
        end
 
-       # Create a new empty string with a given capacity.
-       init with_capacity(cap: Int)
+       redef fun *(repeats)
        do
-               assert cap >= 0
-               # _items = new NativeString.calloc(cap)
-               _items = calloc_string(cap+1)
-               _capacity = cap
-               _length = 0
+               var new_buf = new FlatBuffer.with_capacity(self.length * repeats)
+               for i in [0..repeats[ do
+                       new_buf.append(self)
+               end
+               return new_buf
        end
 
-       redef fun ==(o)
+       redef fun to_upper
        do
-               if not o isa Buffer or o is null 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
+               var new_buf = new FlatBuffer.with_capacity(self.length)
+               for i in self.chars do
+                       new_buf.add(i.to_upper)
                end
-               return true
+               return new_buf
        end
 
-       readable private var _capacity: Int 
+       redef fun to_lower
+       do
+               var new_buf = new FlatBuffer.with_capacity(self.length)
+               for i in self.chars do
+                       new_buf.add(i.to_lower)
+               end
+               return new_buf
+       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
+
+end
+
+private class FlatBufferCharView
+       super BufferCharView
+       super StringCapable
+
+       redef type SELFTYPE: FlatBuffer
+
+       redef fun [](index) do return target.items[index]
+
+       redef fun []=(index, item)
+       do
+               assert index >= 0 and index <= length
+               if index == length then
+                       add(item)
+                       return
+               end
+               target.items[index] = item
+       end
+
+       redef fun push(c)
+       do
+               target.add(c)
+       end
+
+       redef fun add(c)
+       do
+               target.add(c)
+       end
+
+       fun enlarge(cap: Int)
+       do
+               target.enlarge(cap)
+       end
+
+       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_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: 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 < target.length
+
+       redef fun item do return target_items[curr_pos]
+
+       redef fun next do curr_pos += 1
+
 end
 
 ###############################################################################
@@ -612,19 +1315,18 @@ end
 ###############################################################################
 
 redef class Object
-       # User readable representation of `self'.
+       # User readable representation of `self`.
        fun to_s: String do return inspect
 
        # The class name of the object in NativeString format.
        private fun native_class_name: NativeString is intern
 
        # The class name of the object.
-       # FIXME: real type information is not available at runtime.
-       # Therefore, for instance, an instance of List[Bool] has just
-       # "List" for class_name
-       fun class_name: String do return new String.from_cstring(native_class_name)
+       #
+       #    assert 5.class_name == "Int"
+       fun class_name: String do return native_class_name.to_s
 
-       # Developer readable representation of `self'.
+       # Developer readable representation of `self`.
        # Usually, it uses the form "<CLASSNAME:#OBJECTID bla bla bla>"
        fun inspect: String
        do
@@ -645,65 +1347,94 @@ redef class Object
 end
 
 redef class Bool
+       #     assert true.to_s         == "true"
+       #     assert false.to_s        == "false"
        redef fun to_s
-       do 
-               if self then 
-                       return once "true" 
-               else 
-                       return once "false" 
+       do
+               if self then
+                       return once "true"
+               else
+                       return once "false"
                end
-       end   
+       end
 end
 
 redef class Int
-       fun fill_buffer(s: Buffer, base: Int, signed: Bool)
-       # Fill `s' with the digits in base 'base' of `self' (and with the '-' sign if 'signed' and negative).
+
+       # 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
+       private fun fill_buffer(s: Buffer, base: Int, signed: Bool)
        do
                var n: Int
                # Sign
                if self < 0 then
                        n = - self
-                       s[0] = '-'
+                       s.chars[0] = '-'
                else if self == 0 then
-                       s[0] = '0'
+                       s.chars[0] = '0'
                        return
                else
                        n = self
                end
                # Fill digits
                var pos = digit_count(base) - 1
-               while pos >= 0 and n > 0 do 
-                       s[pos] = (n % base).to_c
+               while pos >= 0 and n > 0 do
+                       s.chars[pos] = (n % base).to_c
                        n = n / base # /
                        pos -= 1
                end
        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"
+
        # return displayable int in base 10 and signed
-       redef fun to_s do return to_base(10,true)
-       
-       # return displayable int in hexadecimal (unsigned (not now))
+       #
+       #     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)
+       end
+
+       # 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 needed decimals up to a max of 6.
+       # Pretty print self, print needoed decimals up to a max of 3.
+       #
+       #     assert 12.34.to_s        == "12.34"
+       #     assert (-0120.03450).to_s  == "-120.035"
+       #
+       # see `to_precision` for a different precision.
        redef fun to_s do
-               var str = to_precision( 6 )
+               var str = to_precision( 3 )
+               if is_inf != 0 or is_nan then return str
                var len = str.length
                for i in [0..len-1] do
                        var j = len-1-i
-                       var c = str[j]
+                       var c = str.chars[j]
                        if c == '0' then
                                continue
                        else if c == '.' then
@@ -715,8 +1446,51 @@ redef class Float
                return str
        end
 
-       # `self' representation with `nb' digits after the '.'.
-       fun to_precision(nb: Int): String import String::from_cstring `{
+       # `self` representation with `nb` digits after the '.'.
+       #
+       #     assert 12.345.to_precision(1) == "12.3"
+       #     assert 12.345.to_precision(2) == "12.35"
+       #     assert 12.345.to_precision(3) == "12.345"
+       #     assert 12.345.to_precision(4) == "12.3450"
+       fun to_precision(nb: Int): String
+       do
+               if is_nan then return "nan"
+
+               var isinf = self.is_inf
+               if isinf == 1 then
+                       return "inf"
+               else if isinf == -1 then
+                       return  "-inf"
+               end
+
+               if nb == 0 then return self.to_i.to_s
+               var f = self
+               for i in [0..nb[ 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
+               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
+               else
+                       return "0." + ("0"*(nb-sl)) + s
+               end
+       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;
 
@@ -724,40 +1498,51 @@ redef class Float
                str = malloc(size + 1);
                sprintf(str, "%.*f", (int)nb, recv );
 
-               return new_String_from_cstring( str );
+               return NativeString_to_s( str );
        `}
 end
 
 redef class Char
+       #     assert 'x'.to_s    == "x"
        redef fun to_s
        do
-               var s = new Buffer.with_capacity(1)
-               s[0] = self
+               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
 
@@ -765,23 +1550,26 @@ 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
 
-       # Concatenate and separate each elements with `sep'. 
-       fun join(sep: String): String
+       # Concatenate and separate each elements with `sep`.
+       #
+       #     assert [1, 2, 3].join(":")         == "1:2:3"
+       #     assert [1..3].join(":")            == "1:2:3"
+       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
                var e = i.item
                if e != null then s.append(e.to_s)
-               
+
                # Concat other items
                i.next
                while i.is_ok do
@@ -798,7 +1586,7 @@ redef class Array[E]
        # Fast implementation
        redef fun to_s
        do
-               var s = new Buffer
+               var s = new FlatBuffer
                var i = 0
                var l = length
                while i < l do
@@ -812,27 +1600,32 @@ end
 
 redef class Map[K,V]
        # Concatenate couple of 'key value'.
-       # key and value are separated by 'couple_sep'.
-       # each couple is separated each couple with `sep'.
+       # key and value are separated by `couple_sep`.
+       # each couple is separated each couple with `sep`.
+       #
+       #     var m = new ArrayMap[Int, String]
+       #     m[1] = "one"
+       #     m[10] = "ten"
+       #     assert m.join("; ", "=") == "1=one; 10=ten"
        fun join(sep: String, couple_sep: String): String
        do
                if is_empty then return ""
-               
-               var s = new Buffer # Result
+
+               var s = new FlatBuffer # Result
 
                # Concat first item
                var i = iterator
                var k = i.key
                var e = i.item
-               if e != null then s.append("{k}{couple_sep}{e}")
-               
+               s.append("{k}{couple_sep}{e or else "<null>"}")
+
                # Concat other items
                i.next
                while i.is_ok do
                        s.append(sep)
                        k = i.key
                        e = i.item
-                       if e != null then s.append("{k}{couple_sep}{e}")
+                       s.append("{k}{couple_sep}{e or else "<null>"}")
                        i.next
                end
                return s.to_s
@@ -845,10 +1638,12 @@ end
 
 # Native strings are simple C char *
 class NativeString
+       super StringCapable
+
        fun [](index: Int): Char is intern
        fun []=(index: Int, item: Char) is intern
        fun copy_to(dest: NativeString, length: Int, from: Int, to: Int) is intern
-       
+
        # Position of the first nul character.
        fun cstring_length: Int
        do
@@ -858,6 +1653,26 @@ class NativeString
        end
        fun atoi: Int is intern
        fun atof: Float is extern "atof"
+
+       redef fun to_s
+       do
+               return to_s_with_length(cstring_length)
+       end
+
+       fun to_s_with_length(length: Int): FlatString
+       do
+               assert length >= 0
+               return new FlatString.with_infos(self, length, 0, length - 1)
+       end
+
+       fun to_s_with_copy: FlatString
+       do
+               var length = cstring_length
+               var new_self = calloc_string(length + 1)
+               copy_to(new_self, length, 0, 0)
+               return new FlatString.with_infos(new_self, length, 0, length - 1)
+       end
+
 end
 
 # StringCapable objects can create native strings
@@ -877,24 +1692,70 @@ redef class Sys
        # The name of the program as given by the OS
        fun program_name: String
        do
-               return new String.from_cstring(native_argv(0))
+               return native_argv(0).to_s
        end
 
-       # Initialize `args' with the contents of `native_argc' and `native_argv'.
+       # Initialize `args` with the contents of `native_argc` and `native_argv`.
        private fun init_args
        do
                var argc = native_argc
                var args = new Array[String].with_capacity(0)
                var i = 1
                while i < argc do
-                       args[i-1] = new String.from_cstring(native_argv(i))
+                       args[i-1] = native_argv(i).to_s
                        i += 1
                end
                _args_cache = args
        end
 
-       private fun native_argc: Int is extern "kernel_Sys_Sys_native_argc_0" # First argument of the main C function.
-       
-       private fun native_argv(i: Int): NativeString is extern "kernel_Sys_Sys_native_argv_1" # Second argument of the main C function.
+       # First argument of the main C function.
+       private fun native_argc: Int is intern
+
+       # Second argument of the main C function.
+       private fun native_argv(i: Int): NativeString is intern
+end
+
+# Comparator that efficienlty use `to_s` to compare things
+#
+# The comparaison call `to_s` on object and use the result to order things.
+#
+#     var a = [1, 2, 3, 10, 20]
+#     (new CachedAlphaComparator).sort(a)
+#     assert a == [1, 10, 2, 20, 3]
+#
+# Internally the result of `to_s` is cached in a HashMap to counter
+# uneficient implementation of `to_s`.
+#
+# Note: it caching is not usefull, see `alpha_comparator`
+class CachedAlphaComparator
+       super Comparator[Object]
+
+       private var cache = new HashMap[Object, String]
+
+       private fun do_to_s(a: Object): String do
+               if cache.has_key(a) then return cache[a]
+               var res = a.to_s
+               cache[a] = res
+               return res
+       end
+
+       redef fun compare(a, b) do
+               return do_to_s(a) <=> do_to_s(b)
+       end
 end
 
+# see `alpha_comparator`
+private class AlphaComparator
+       super Comparator[Object]
+       redef fun compare(a, b) do return a.to_s <=> b.to_s
+end
+
+# Stateless comparator that naively use `to_s` to compare things.
+#
+# Note: the result of `to_s` is not cached, thus can be invoked a lot
+# on a single instace. See `CachedAlphaComparator` as an alternative.
+#
+#     var a = [1, 2, 3, 10, 20]
+#     alpha_comparator.sort(a)
+#     assert a == [1, 10, 2, 20, 3]
+fun alpha_comparator: Comparator[Object] do return once new AlphaComparator