1 package Encode::Encoding;
2 # Base class for classes which implement encodings
4 our $VERSION = do { my @r = (q$Revision: 1.25 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
10 $obj = bless { Name => $canonical },$obj unless ref $obj;
11 # warn "$canonical => $obj\n";
12 Encode::define_encoding($obj, $canonical, @_);
15 sub name { shift->{'Name'} }
17 # Temporary legacy methods
18 sub toUnicode { shift->decode(@_) }
19 sub fromUnicode { shift->encode(@_) }
21 sub new_sequence { return $_[0] }
32 Encode::Encoding - Encode Implementation Base Class
36 package Encode::MyEncoding;
37 use base qw(Encode::Encoding);
39 __PACKAGE__->Define(qw(myCanonical myAlias));
43 As mentioned in L<Encode>, encodings are (in the current
44 implementation at least) defined by objects. The mapping of encoding
45 name to object is via the C<%encodings> hash.
47 The values of the hash can currently be either strings or objects.
48 The string form may go away in the future. The string form occurs
49 when C<encodings()> has scanned C<@INC> for loadable encodings but has
50 not actually loaded the encoding in question. This is because the
51 current "loading" process is all Perl and a bit slow.
53 Once an encoding is loaded then value of the hash is object which
54 implements the encoding. The object should provide the following
61 Should return the string representing the canonical name of the encoding.
63 =item -E<gt>new_sequence
65 This is a placeholder for encodings with state. It should return an
66 object which implements this interface, all current implementations
67 return the original object.
69 =item -E<gt>encode($string,$check)
71 Should return the octet sequence representing I<$string>. If I<$check>
72 is true it should modify I<$string> in place to remove the converted
73 part (i.e. the whole string unless there is an error). If an error
74 occurs it should return the octet sequence for the fragment of string
75 that has been converted, and modify $string in-place to remove the
76 converted part leaving it starting with the problem fragment.
78 If check is is false then C<encode> should make a "best effort" to
79 convert the string - for example by using a replacement character.
81 =item -E<gt>decode($octets,$check)
83 Should return the string that I<$octets> represents. If I<$check> is
84 true it should modify I<$octets> in place to remove the converted part
85 (i.e. the whole sequence unless there is an error). If an error
86 occurs it should return the fragment of string that has been
87 converted, and modify $octets in-place to remove the converted part
88 leaving it starting with the problem fragment.
90 If check is is false then C<decode> should make a "best effort" to
91 convert the string - for example by using Unicode's "\x{FFFD}" as a
92 replacement character.
96 It should be noted that the check behaviour is different from the
97 outer public API. The logic is that the "unchecked" case is useful
98 when encoding is part of a stream which may be reporting errors
99 (e.g. STDERR). In such cases it is desirable to get everything
100 through somehow without causing additional errors which obscure the
101 original one. Also the encoding is best placed to know what the
102 correct replacement character is, so if that is the desired behaviour
103 then letting low level code do it is the most efficient.
105 In contrast if check is true, the scheme above allows the encoding to
106 do as much as it can and tell layer above how much that was. What is
107 lacking at present is a mechanism to report what went wrong. The most
108 likely interface will be an additional method call to the object, or
109 perhaps (to avoid forcing per-stream objects on otherwise stateless
110 encodings) and additional parameter.
112 It is also highly desirable that encoding classes inherit from
113 C<Encode::Encoding> as a base class. This allows that class to define
114 additional behaviour for all encoding objects. For example built in
115 Unicode, UCS-2 and UTF-8 classes use :
117 package Encode::MyEncoding;
118 use base qw(Encode::Encoding);
120 __PACKAGE__->Define(qw(myCanonical myAlias));
122 To create an object with bless {Name => ...},$class, and call
123 define_encoding. They inherit their C<name> method from
126 =head2 Compiled Encodings
128 For the sake of speed and efficiency, Most of the encodings are now
129 supported via I<Compiled Form> that are XS modules generated from UCM
130 files. Encode provides enc2xs tool to achieve that. Please see
131 L<enc2xs> for more details.
135 L<perlmod>, L<enc2xs>
144 Passed remaining fragment of string being processed.
145 Modifies it in place to remove bytes/characters it can understand
146 and returns a string used to represent them.
150 my $ch = substr($_[0],0,1,'');
151 return sprintf("\x{%02X}",ord($ch);
154 This scheme is close to how underlying C code for Encode works, but gives
155 the fixup routine very little context.
159 Passed original string, and an index into it of the problem area, and
160 output string so far. Appends what it will to output string and
161 returns new index into original string. For example:
164 # my ($s,$i,$d) = @_;
165 my $ch = substr($_[0],$_[1],1);
166 $_[2] .= sprintf("\x{%02X}",ord($ch);
170 This scheme gives maximal control to the fixup routine but is more
171 complicated to code, and may need internals of Encode to be tweaked to
172 keep original string intact.
178 Multiple return values rather than in-place modifications.
180 Index into the string could be C<pos($str)> allowing C<s/\G...//>.