lib/string: redefine [] for FlatString and FlatBuffer without using chars
[nit.git] / lib / standard / string.nit
index ff18a7d..e4423d3 100644 (file)
 module string
 
 import math
-intrude import collection # FIXME should be collection::array
+import collection
 
 `{
 #include <stdio.h>
+#include <string.h>
 `}
 
 ###############################################################################
@@ -32,18 +33,18 @@ abstract class Text
 
        redef type OTHER: Text
 
-       # Type of the view on self (.chars)
-       type SELFVIEW: StringCharView
-
        # Type of self (used for factorization of several methods, ex : substring_from, empty...)
        type SELFTYPE: Text
 
-       var hash_cache: nullable Int = null
-
        # Gets a view on the chars of the Text object
-       fun chars: SELFVIEW is abstract
+       #
+       #     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.
@@ -58,19 +59,20 @@ abstract class Text
        # In this case, `from += count` and `count -= from`.
        fun substring(from: Int, count: Int): SELFTYPE is abstract
 
-       # Concatenates `o` to `self`
-       fun +(o: Text): SELFTYPE is abstract
-
-       # Auto-concatenates self `i` times
-       fun *(i: 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
+       #
+       #     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
-       fun empty: SELFTYPE is abstract
+       #
+       # 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
        #
@@ -109,6 +111,7 @@ abstract class Text
                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
@@ -127,9 +130,10 @@ abstract class Text
        fun to_cstring: NativeString do return flatten.to_cstring
 
        # The index of the last occurrence of an element starting from pos (in reverse order).
-       # Example :
-       #               assert "/etc/bin/test/test.nit".last_index_of_from('/', length-1) == 13
-       #               assert "/etc/bin/test/test.nit".last_index_of_from('/', 12) == 8
+       #
+       #     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
        #
@@ -179,9 +183,6 @@ abstract class Text
                return substring(from, length - from)
        end
 
-       # Returns a reversed version of self
-       fun reversed: SELFTYPE is abstract
-
        # Does self have a substring `str` starting from position `pos`?
        #
        #     assert "abcd".has_substring("bc",1)            ==  true
@@ -189,7 +190,7 @@ abstract class Text
        fun has_substring(str: String, pos: Int): Bool
        do
                var myiter = self.chars.iterator_from(pos)
-               var itsiter = str.iterator
+               var itsiter = str.chars.iterator
                while myiter.is_ok and itsiter.is_ok do
                        if myiter.item != itsiter.item then return false
                        myiter.next
@@ -234,6 +235,8 @@ abstract class Text
        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
@@ -244,8 +247,8 @@ abstract class Text
                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
@@ -275,12 +278,10 @@ abstract class Text
        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
@@ -290,17 +291,56 @@ abstract class Text
                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: SELFTYPE is abstract
+       #     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
 
-       # A lower case version of `self`
+       # Are all letters in `self` upper-case ?
        #
-       #     assert "Hello World!".to_lower     == "hello world!"
-       fun to_lower : SELFTYPE is abstract
+       #     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 iter = self.chars.iterator
@@ -313,6 +353,10 @@ abstract class Text
        end
 
        # 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 iter = self.chars.reverse_iterator
@@ -336,7 +380,8 @@ abstract class Text
        do
                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
@@ -369,7 +414,8 @@ abstract class Text
        fun escape_to_c: String
        do
                var b = new FlatBuffer
-               for c in self.chars do
+               for i in [0..length[ do
+                       var c = chars[i]
                        if c == '\n' then
                                b.append("\\n")
                        else if c == '\0' then
@@ -396,7 +442,7 @@ abstract class Text
        fun escape_more_to_c(chars: String): String
        do
                var b = new FlatBuffer
-               for c in escape_to_c do
+               for c in escape_to_c.chars do
                        if chars.chars.has(c) then
                                b.add('\\')
                        end
@@ -405,24 +451,24 @@ abstract class Text
                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("\{\}")
 
        # 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 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
@@ -447,6 +493,111 @@ abstract class Text
                return res.to_s
        end
 
+       # 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
+
+               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
+
+               return buf.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
@@ -456,24 +607,43 @@ abstract class Text
                return self.chars == o.chars
        end
 
-       redef fun <(o)
+       # Lexicographical comparaison
+       #
+       #     assert "abc" < "xy"
+       #     assert "ABC" < "abc"
+       redef fun <(other)
        do
-               return self.chars < o.chars
+               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
-                       var i = length - 1
 
-                       for char in self.chars do
-                               h = (h * 32) + h + char.ascii
-                               i -= 1
+                       for i in [0..length[ do
+                               var char = chars[i]
+                               h = h.lshift(5) + h + char.ascii
                        end
 
                        hash_cache = h
@@ -492,7 +662,7 @@ abstract class FlatText
        # Real items, used as cache for to_cstring is called
        private var real_items: nullable NativeString = null
 
-       redef var length: Int
+       redef var length: Int = 0
 
        init do end
 
@@ -510,14 +680,11 @@ end
 
 # Abstract class for the SequenceRead compatible
 # views on String and Buffer objects
-abstract class StringCharView
+private abstract class StringCharView
        super SequenceRead[Char]
-       super Comparable
 
        type SELFTYPE: Text
 
-       redef type OTHER: StringCharView
-
        private var target: SELFTYPE
 
        private init(tgt: SELFTYPE)
@@ -531,99 +698,149 @@ abstract class StringCharView
 
        redef fun iterator: IndexedIterator[Char] do return self.iterator_from(0)
 
-       # Gets a new Iterator starting at position `pos`
-       #
-       # Ex :
-       #       var iter = "abcd".iterator_from(2)
-       #       while iter.is_ok do
-       #               printn iter.item
-       #               iter.next
-       #       end
-       #
-       # Outputs : cd
-       fun iterator_from(pos: Int): IndexedIterator[Char] is abstract
+       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
 
-       # Gets an iterator starting at the end and going backwards
+abstract class String
+       super Text
+
+       redef type SELFTYPE: String
+
+       redef fun to_s do return self
+
+       # Concatenates `o` to `self`
        #
-       # Ex :
-       #       var reviter = "now step live...".reverse_iterator
-       #       while reviter.is_ok do
-       #               printn reviter.item
-       #               reviter.next
-       #       end
+       #     assert "hello" + "world"  == "helloworld"
+       #     assert "" + "hello" + ""  == "hello"
+       fun +(o: Text): SELFTYPE is abstract
+
+       # Concatenates self `i` times
        #
-       # Outputs : ...evil pets won
-       fun reverse_iterator: IndexedIterator[Char] do return self.reverse_iterator_from(self.length - 1)
+       #     assert "abc" * 4 == "abcabcabcabc"
+       #     assert "abc" * 1 == "abc"
+       #     assert "abc" * 0 == ""
+       fun *(i: Int): SELFTYPE is abstract
+
+       fun insert_at(s: String, pos: Int): SELFTYPE is abstract
 
-       # Gets an iterator on the chars of self starting from `pos`
+       # Returns a reversed version of self
        #
-       # Ex :
-       #       var iter = "abcd".reverse_iterator_from(1)
-       #       while iter.is_ok do
-       #               printn iter.item
-       #               iter.next
-       #       end
+       #     assert "hello".reversed  == "olleh"
+       #     assert "bob".reversed    == "bob"
+       #     assert "".reversed       == ""
+       fun reversed: SELFTYPE is abstract
+
+       # A upper case version of `self`
        #
-       # Outputs : ba
-       fun reverse_iterator_from(pos: Int): IndexedIterator[Char] is abstract
+       #     assert "Hello World!".to_upper     == "HELLO WORLD!"
+       fun to_upper: SELFTYPE is abstract
 
-       redef fun has(c: Char): Bool
-       do
-               for i in self do
-                       if i == c then return true
-               end
-               return false
-       end
+       # A lower case version of `self`
+       #
+       #     assert "Hello World!".to_lower     == "hello world!"
+       fun to_lower : SELFTYPE is abstract
 
-       redef fun ==(other)
-       do
-               if other == null then return false
-               if not other isa StringCharView then return false
-               var other_chars = other.iterator
-               for i in self do
-                       if i != other_chars.item then return false
-                       other_chars.next
+       # 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 true
+               
+               return new_str.to_s
        end
 
-       redef fun <(other)
-       do
-               var self_chars = self.iterator
-               var other_chars = other.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
+       # 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
 
-               if self_chars.is_ok then
-                       return false
-               else
-                       return true
-               end
+               return new_str.to_s
        end
 end
 
-# View on Buffer objects, extends Sequence
-# for mutation operations
-abstract class BufferCharView
-       super StringCharView
-       super Sequence[Char]
+private class FlatSubstringsIter
+       super Iterator[FlatText]
 
-       redef type SELFTYPE: Buffer
+       var tgt: nullable FlatText
 
-end
+       init(tgt: FlatText) do self.tgt = tgt
 
-abstract class String
-       super Text
-
-       redef type SELFTYPE: String
+       redef fun item do
+               assert is_ok
+               return tgt.as(not null)
+       end
 
-       redef fun to_s do return self
+       redef fun is_ok do return tgt != null
 
+       redef fun next do tgt = null
 end
 
 # Immutable strings of characters.
@@ -631,38 +848,38 @@ class FlatString
        super FlatText
        super String
 
-       redef type SELFTYPE: FlatString
-       redef type SELFVIEW: FlatStringCharView
-
        # Index in _items of the start of the string
        private var index_from: Int
 
        # Indes in _items of the last item of the string
        private var index_to: Int
 
-       redef var chars: SELFVIEW = new FlatStringCharView(self)
-
-       ################################################
-       #       AbstractString specific methods        #
-       ################################################
+       redef var chars: SequenceRead[Char] = new FlatStringCharView(self)
 
-       redef fun [](index) do
-               assert index >= 0
+       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 reversed
        do
                var native = calloc_string(self.length + 1)
-               var reviter = chars.reverse_iterator
+               var length = self.length
+               var items = self.items
                var pos = 0
-               while reviter.is_ok do
-                       native[pos] = reviter.item
+               var ipos = length-1
+               while pos < length do
+                       native[pos] = items[ipos]
                        pos += 1
-                       reviter.next
+                       ipos -= 1
                end
                return native.to_s_with_length(self.length)
        end
@@ -752,7 +969,6 @@ class FlatString
                index_to = to
        end
 
-       # Return a null terminated char *
        redef fun to_cstring: NativeString
        do
                if real_items != null then return real_items.as(not null)
@@ -793,9 +1009,6 @@ class FlatString
                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
@@ -832,9 +1045,6 @@ class FlatString
                return my_length < its_length
        end
 
-       # The concatenation of `self` with `s`
-       #
-       #     assert "hello " + "world!"         == "hello world!"
        redef fun +(s)
        do
                var my_length = self.length
@@ -851,8 +1061,9 @@ class FlatString
                        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
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               target_string[curr_pos] = c
                                curr_pos += 1
                        end
                end
@@ -862,9 +1073,6 @@ class FlatString
                return target_string.to_s_with_length(total_length)
        end
 
-       #     assert "abc"*3           == "abcabcabc"
-       #     assert "abc"*1           == "abc"
-       #     assert "abc"*0           == ""
        redef fun *(i)
        do
                assert i >= 0
@@ -892,18 +1100,15 @@ class FlatString
        redef fun hash
        do
                if hash_cache == null then
-                       # djb2 hash algorythm
+                       # djb2 hash algorithm
                        var h = 5381
-                       var i = length - 1
+                       var i = index_from
 
                        var myitems = items
-                       var strStart = index_from
-
-                       i += strStart
 
-                       while i >= strStart do
-                               h = (h * 32) + h + self.items[i].ascii
-                               i -= 1
+                       while i <= index_to do
+                               h = h.lshift(5) + h + myitems[i].ascii
+                               i += 1
                        end
 
                        hash_cache = h
@@ -911,6 +1116,8 @@ class FlatString
 
                return hash_cache.as(not null)
        end
+
+       redef fun substrings do return new FlatSubstringsIter(self)
 end
 
 private class FlatStringReverseIterator
@@ -975,6 +1182,7 @@ private class FlatStringCharView
                # 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
@@ -988,9 +1196,11 @@ end
 abstract class Buffer
        super Text
 
-       redef type SELFVIEW: BufferCharView
        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
@@ -1002,14 +1212,66 @@ abstract class Buffer
        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
+
+       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.
@@ -1017,15 +1279,24 @@ class FlatBuffer
        super FlatText
        super Buffer
 
-       redef type SELFVIEW: FlatBufferCharView
        redef type SELFTYPE: FlatBuffer
 
-       redef var chars: SELFVIEW = new FlatBufferCharView(self)
+       redef var chars: Sequence[Char] = new FlatBufferCharView(self)
+
+       private var capacity: Int = 0
 
-       var capacity: Int
+       redef fun substrings do return new FlatSubstringsIter(self)
+
+       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
@@ -1036,12 +1307,16 @@ class FlatBuffer
 
        redef fun add(c)
        do
+               is_dirty = true
                if capacity <= length then enlarge(length + 5)
                items[length] = c
                length += 1
        end
 
-       redef fun clear do length = 0
+       redef fun clear do
+               is_dirty = true
+               length = 0
+       end
 
        redef fun empty do return new FlatBuffer
 
@@ -1051,40 +1326,30 @@ class FlatBuffer
                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)
+               if length > 0 then items.copy_to(a, length, 0, 0)
                items = a
                capacity = c
-               items.copy_to(a, length, 0, 0)
        end
 
        redef fun to_s: String
        do
-               var l = length
-               var a = calloc_string(l+1)
-               items.copy_to(a, l, 0, 0)
-
-               # Ensure the afterlast byte is '\0' to nul-terminated char *
-               a[length] = '\0'
-
-               return a.to_s_with_length(length)
+               return to_cstring.to_s_with_length(length)
        end
 
        redef fun to_cstring
        do
-               if real_items == null then
+               if is_dirty then
                        var new_native = calloc_string(length + 1)
                        new_native[length] = '\0'
-                       items.copy_to(new_native, length, 0, 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
-               with_capacity(5)
-       end
+       init do end
 
        init from(s: Text)
        do
@@ -1097,8 +1362,9 @@ class FlatBuffer
                        s.items.copy_to(items, length, 0, 0)
                else
                        var curr_pos = 0
-                       for i in s.chars do
-                               items[curr_pos] = i
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               items[curr_pos] = c
                                curr_pos += 1
                        end
                end
@@ -1116,6 +1382,8 @@ class FlatBuffer
 
        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
@@ -1124,8 +1392,9 @@ class FlatBuffer
                        s.items.copy_to(items, sl, 0, length)
                else
                        var curr_pos = self.length
-                       for i in s.chars do
-                               items[curr_pos] = i
+                       for i in [0..s.length[ do
+                               var c = s.chars[i]
+                               items[curr_pos] = c
                                curr_pos += 1
                        end
                end
@@ -1160,32 +1429,46 @@ class FlatBuffer
                end
        end
 
-       redef fun reversed
+       redef fun reverse
+       do
+               var ns = calloc_string(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
+
+       redef fun times(repeats)
        do
-               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
+               var x = new FlatString.with_infos(items, length, 0, length - 1)
+               for i in [1..repeats[ do
+                       append(x)
                end
-               return new_buf
        end
 
-       redef fun +(other)
+       redef fun upper
        do
-               var new_buf = new FlatBuffer.with_capacity(self.length + other.length)
-               new_buf.append(self)
-               new_buf.append(other)
-               return new_buf
+               var it = items
+               var id = length - 1
+               while id >= 0 do
+                       it[id] = it[id].to_upper
+                       id -= 1
+               end
        end
 
-       redef fun *(repeats)
+       redef fun lower
        do
-               var new_buf = new FlatBuffer.with_capacity(self.length * repeats)
-               for i in [0..repeats[ do
-                       new_buf.append(self)
+               var it = items
+               var id = length - 1
+               while id >= 0 do
+                       it[id] = it[id].to_lower
+                       id -= 1
                end
-               return new_buf
        end
 end
 
@@ -1201,7 +1484,7 @@ private class FlatBufferReverseIterator
        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
 
@@ -1273,7 +1556,7 @@ private class FlatBufferIterator
        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
 
@@ -1316,11 +1599,6 @@ 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
@@ -1337,9 +1615,18 @@ 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
@@ -1362,18 +1649,20 @@ 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
@@ -1388,6 +1677,11 @@ end
 
 redef class Float
        # 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( 3 )
                if is_inf != 0 or is_nan then return str
@@ -1407,6 +1701,11 @@ redef class Float
        end
 
        # `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"
@@ -1439,6 +1738,12 @@ redef class Float
                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;
@@ -1461,27 +1766,37 @@ redef class Char
        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
 
@@ -1498,7 +1813,7 @@ 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 ""
 
@@ -1576,7 +1891,7 @@ end
 ###############################################################################
 
 # Native strings are simple C char *
-class NativeString
+extern class NativeString `{ char* `}
        super StringCapable
 
        fun [](index: Int): Char is intern
@@ -1611,7 +1926,6 @@ class NativeString
                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
@@ -1622,7 +1936,8 @@ end
 redef class Sys
        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)
@@ -1634,7 +1949,7 @@ 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
@@ -1654,3 +1969,53 @@ redef class Sys
        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
+
+# The arguments of the program as given by the OS
+fun args: Sequence[String]
+do
+       return sys.program_args
+end