Encode::Encoding(3pm)

1Encode::Encoding(3)   User Contributed Perl Documentation  Encode::Encoding(3)
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NAME

6       Encode::Encoding - Encode Implementation Base Class
7

SYNOPSIS

9         package Encode::MyEncoding;
10         use base qw(Encode::Encoding);
11
12         __PACKAGE__->Define(qw(myCanonical myAlias));
13

DESCRIPTION

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
21   Methods you should implement
22       You are strongly encouraged to implement methods below, at least either
23       encode() or decode().
24
25       ->encode($string [,$check])
26           MUST return the octet sequence representing $string.
27
28           · If $check is true, it SHOULD modify $string in place to remove
29             the converted part (i.e.  the whole string unless there is an
30             error).  If perlio_ok() is true, SHOULD becomes MUST.
31
32           · If an error occurs, it SHOULD return the octet sequence for the
33             fragment of string that has been converted and modify $string in-
34             place to remove the converted part leaving it starting with the
35             problem fragment.  If perlio_ok() is true, SHOULD becomes MUST.
36
37           · If $check is is false then "encode" MUST  make a "best effort" to
38             convert the string - for example, by using a replacement
39             character.
40
41       ->decode($octets [,$check])
42           MUST return the string that $octets represents.
43
44           · If $check is true, it SHOULD modify $octets in place to remove
45             the converted part (i.e.  the whole sequence unless there is an
46             error).  If perlio_ok() is true, SHOULD becomes MUST.
47
48           · If an error occurs, it SHOULD return the fragment of string that
49             has been converted and modify $octets in-place to remove the
50             converted part leaving it starting with the problem fragment.  If
51             perlio_ok() is true, SHOULD becomes MUST.
52
53           · If $check is false then "decode" should make a "best effort" to
54             convert the string - for example by using Unicode's "\x{FFFD}" as
55             a replacement character.
56
57       If you want your encoding to work with encoding pragma, you should also
58       implement the method below.
59
60       ->cat_decode($destination, $octets, $offset, $terminator [,$check])
61           MUST decode $octets with $offset and concatenate it to
62           $destination.  Decoding will terminate when $terminator (a string)
63           appears in output.  $offset will be modified to the last $octets
64           position at end of decode.  Returns true if $terminator appears
65           output, else returns false.
66
67   Other methods defined in Encode::Encodings
68       You do not have to override methods shown below unless you have to.
69
70       ->name
71           Predefined As:
72
73             sub name  { return shift->{'Name'} }
74
75           MUST return the string representing the canonical name of the
76           encoding.
77
78       ->mime_name
79           Predefined As:
80
81             sub mime_name{
82               require Encode::MIME::Name;
83               return Encode::MIME::Name::get_mime_name(shift->name);
84             }
85
86           MUST return the string representing the IANA charset name of the
87           encoding.
88
89       ->renew
90           Predefined As:
91
92             sub renew {
93               my $self = shift;
94               my $clone = bless { %$self } => ref($self);
95               $clone->{renewed}++;
96               return $clone;
97             }
98
99           This method reconstructs the encoding object if necessary.  If you
100           need to store the state during encoding, this is where you clone
101           your object.
102
103           PerlIO ALWAYS calls this method to make sure it has its own private
104           encoding object.
105
106       ->renewed
107           Predefined As:
108
109             sub renewed { $_[0]->{renewed} || 0 }
110
111           Tells whether the object is renewed (and how many times).  Some
112           modules emit "Use of uninitialized value in null operation" warning
113           unless the value is numeric so return 0 for false.
114
115       ->perlio_ok()
116           Predefined As:
117
118             sub perlio_ok {
119                 eval{ require PerlIO::encoding };
120                 return $@ ? 0 : 1;
121             }
122
123           If your encoding does not support PerlIO for some reasons, just;
124
125            sub perlio_ok { 0 }
126
127       ->needs_lines()
128           Predefined As:
129
130             sub needs_lines { 0 };
131
132           If your encoding can work with PerlIO but needs line buffering, you
133           MUST define this method so it returns true.  7bit ISO-2022
134           encodings are one example that needs this.  When this method is
135           missing, false is assumed.
136
137   Example: Encode::ROT13
138         package Encode::ROT13;
139         use strict;
140         use base qw(Encode::Encoding);
141
142         __PACKAGE__->Define('rot13');
143
144         sub encode($$;$){
145             my ($obj, $str, $chk) = @_;
146             $str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
147             $_[1] = '' if $chk; # this is what in-place edit means
148             return $str;
149         }
150
151         # Jr pna or ynml yvxr guvf;
152         *decode = \&encode;
153
154         1;
155

Why the heck Encode API is different?

157       It should be noted that the $check behaviour is different from the
158       outer public API. The logic is that the "unchecked" case is useful when
159       the encoding is part of a stream which may be reporting errors (e.g.
160       STDERR).  In such cases, it is desirable to get everything through
161       somehow without causing additional errors which obscure the original
162       one. Also, the encoding is best placed to know what the correct
163       replacement character is, so if that is the desired behaviour then
164       letting low level code do it is the most efficient.
165
166       By contrast, if $check is true, the scheme above allows the encoding to
167       do as much as it can and tell the layer above how much that was. What
168       is lacking at present is a mechanism to report what went wrong. The
169       most likely interface will be an additional method call to the object,
170       or perhaps (to avoid forcing per-stream objects on otherwise stateless
171       encodings) an additional parameter.
172
173       It is also highly desirable that encoding classes inherit from
174       "Encode::Encoding" as a base class. This allows that class to define
175       additional behaviour for all encoding objects.
176
177         package Encode::MyEncoding;
178         use base qw(Encode::Encoding);
179
180         __PACKAGE__->Define(qw(myCanonical myAlias));
181
182       to create an object with "bless {Name => ...}, $class", and call
183       define_encoding.  They inherit their "name" method from
184       "Encode::Encoding".
185
186   Compiled Encodings
187       For the sake of speed and efficiency, most of the encodings are now
188       supported via a compiled form: XS modules generated from UCM files.
189       Encode provides the enc2xs tool to achieve that.  Please see enc2xs for
190       more details.
191

NAME

SYNOPSIS

DESCRIPTION

Why the heck Encode API is different?

SEE ALSO