1Encode::Encoding(3pm) Perl Programmers Reference Guide Encode::Encoding(3pm)
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6 Encode::Encoding - Encode Implementation Base Class
7
9 package Encode::MyEncoding;
10 use base qw(Encode::Encoding);
11 __PACKAGE__->Define(qw(myCanonical myAlias));
13
15 As mentioned in Encode, encodings are (in the current implementation at
16 least) defined as objects. The mapping of encoding name to object is
17 via the %Encode::Encoding hash. Though you can directly manipulate
18 this hash, it is strongly encouraged to use this base class module and
19 add encode() and decode() methods.
20 Methods you should implement
22 You are strongly encouraged to implement methods below, at least either
24 encode() or decode().
25 ->encode($string [,$check])
27 MUST return the octet sequence representing $string.
28 * If $check is true, it SHOULD modify $string in place to remove
30 the converted part (i.e. the whole string unless there is an
31 error). If perlio_ok() is true, SHOULD becomes MUST.
32 * If an error occurs, it SHOULD return the octet sequence for the
34 fragment of string that has been converted and modify $string in-
35 place to remove the converted part leaving it starting with the
36 problem fragment. If perlio_ok() is true, SHOULD becomes MUST.
37 * If $check is is false then "encode" MUST make a "best effort" to
39 convert the string - for example, by using a replacement charac‐
40 ter.
41 ->decode($octets [,$check])
43 MUST return the string that $octets represents.
44 * If $check is true, it SHOULD modify $octets in place to remove
46 the converted part (i.e. the whole sequence unless there is an
47 error). If perlio_ok() is true, SHOULD becomes MUST.
48 * If an error occurs, it SHOULD return the fragment of string that
50 has been converted and modify $octets in-place to remove the con‐
51 verted part leaving it starting with the problem fragment. If
52 perlio_ok() is true, SHOULD becomes MUST.
53 * If $check is false then "decode" should make a "best effort" to
55 convert the string - for example by using Unicode's "\x{FFFD}" as
56 a replacement character.
57 If you want your encoding to work with encoding pragma, you should also
59 implement the method below.
60 ->cat_decode($destination, $octets, $offset, $terminator [,$check])
62 MUST decode $octets with $offset and concatenate it to $destina‐
63 tion. Decoding will terminate when $terminator (a string) appears
64 in output. $offset will be modified to the last $octets position
65 at end of decode. Returns true if $terminator appears output, else
66 returns false.
67 Other methods defined in Encode::Encodings
69 You do not have to override methods shown below unless you have to.
71 ->name
73 Predefined As:
74 sub name { return shift->{'Name'} }
76 MUST return the string representing the canonical name of the
78 encoding.
79 ->renew
81 Predefined As:
82 sub renew {
84 my $self = shift;
85 my $clone = bless { %$self } => ref($self);
86 $clone->{renewed}++;
87 return $clone;
88 }
89 This method reconstructs the encoding object if necessary. If you
91 need to store the state during encoding, this is where you clone
92 your object.
93 PerlIO ALWAYS calls this method to make sure it has its own private
95 encoding object.
96 ->renewed
98 Predefined As:
99 sub renewed { $_[0]->{renewed} ⎪⎪ 0 }
101 Tells whether the object is renewed (and how many times). Some
103 modules emit "Use of uninitialized value in null operation" warning
104 unless the value is numeric so return 0 for false.
105 ->perlio_ok()
107 Predefined As:
108 sub perlio_ok {
110 eval{ require PerlIO::encoding };
111 return $@ ? 0 : 1;
112 }
113 If your encoding does not support PerlIO for some reasons, just;
115 sub perlio_ok { 0 }
117 ->needs_lines()
119 Predefined As:
120 sub needs_lines { 0 };
122 If your encoding can work with PerlIO but needs line buffering, you
124 MUST define this method so it returns true. 7bit ISO-2022 encod‐
125 ings are one example that needs this. When this method is missing,
126 false is assumed.
127 Example: Encode::ROT13
129 package Encode::ROT13;
131 use strict;
132 use base qw(Encode::Encoding);
133 __PACKAGE__->Define('rot13');
135 sub encode($$;$){
137 my ($obj, $str, $chk) = @_;
138 $str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
139 $_[1] = '' if $chk; # this is what in-place edit means
140 return $str;
141 }
142 # Jr pna or ynml yvxr guvf;
144 *decode = \&encode;
145 1;
147
149 It should be noted that the $check behaviour is different from the
150 outer public API. The logic is that the "unchecked" case is useful when
151 the encoding is part of a stream which may be reporting errors (e.g.
152 STDERR). In such cases, it is desirable to get everything through
153 somehow without causing additional errors which obscure the original
154 one. Also, the encoding is best placed to know what the correct
155 replacement character is, so if that is the desired behaviour then let‐
156 ting low level code do it is the most efficient.
157 By contrast, if $check is true, the scheme above allows the encoding to
159 do as much as it can and tell the layer above how much that was. What
160 is lacking at present is a mechanism to report what went wrong. The
161 most likely interface will be an additional method call to the object,
162 or perhaps (to avoid forcing per-stream objects on otherwise stateless
163 encodings) an additional parameter.
164 It is also highly desirable that encoding classes inherit from
166 "Encode::Encoding" as a base class. This allows that class to define
167 additional behaviour for all encoding objects.
168 package Encode::MyEncoding;
170 use base qw(Encode::Encoding);
171 __PACKAGE__->Define(qw(myCanonical myAlias));
173 to create an object with "bless {Name => ...}, $class", and call
175 define_encoding. They inherit their "name" method from "Encode::Encod‐
176 ing".
177 Compiled Encodings
179 For the sake of speed and efficiency, most of the encodings are now
181 supported via a compiled form: XS modules generated from UCM files.
182 Encode provides the enc2xs tool to achieve that. Please see enc2xs for
183 more details.
184
186 perlmod, enc2xs
187perl v5.8.8 2001-09-21 Encode::Encoding(3pm)