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man : Encode::Encoding
ext::Encode::lib:PerloPrograemxmte:r:sEnRceofdee::lib::Encode::Encoding(3p)
NAME
Encode::Encoding - Encode Implementation Base Class
SYNOPSIS
package Encode::MyEncoding;
use base qw(Encode::Encoding);
__PACKAGE__->Define(qw(myCanonical myAlias));
DESCRIPTION
As mentioned in Encode, encodings are (in the current
implementation at least) defined as objects. The mapping
of encoding name to object is via the %Encode::Encoding
hash. Though you can directly manipulate this hash, it is
strongly encouraged to use this base class module and add
encode() and decode() methods.
Methods you should implement
You are strongly encouraged to implement methods below, at
least either encode() or decode().
->encode($string [,$check])
MUST return the octet sequence representing $string.
* If $check is true, it SHOULD modify $string in place
to remove the converted part (i.e. the whole string
unless there is an error). If perlio_ok() is true,
SHOULD becomes MUST.
* If an error occurs, it SHOULD return the octet
sequence for the fragment of string that has been
converted and modify $string in-place to remove the
converted part leaving it starting with the problem
fragment. If perlio_ok() is true, SHOULD becomes
MUST.
* If $check is is false then "encode" MUST make a
"best effort" to convert the string - for example,
by using a replacement character.
->decode($octets [,$check])
MUST return the string that $octets represents.
* If $check is true, it SHOULD modify $octets in place
to remove the converted part (i.e. the whole
sequence unless there is an error). If perlio_ok()
is true, SHOULD becomes MUST.
* If an error occurs, it SHOULD return the fragment of
string that has been converted and modify $octets
in-place to remove the converted part leaving it
starting with the problem fragment. If perlio_ok()
is true, SHOULD becomes MUST.
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* If $check is false then "decode" should make a "best
effort" to convert the string - for example by using
Unicode's "\x{FFFD}" as a replacement character.
If you want your encoding to work with encoding pragma,
you should also implement the method below.
->cat_decode($destination, $octets, $offset, $terminator
[,$check])
MUST decode $octets with $offset and concatenate it to
$destination. Decoding will terminate when $termina-
tor (a string) appears in output. $offset will be
modified to the last $octets position at end of
decode. Returns true if $terminator appears output,
else returns false.
Other methods defined in Encode::Encodings
You do not have to override methods shown below unless you
have to.
->name
Predefined As:
sub name { return shift->{'Name'} }
MUST return the string representing the canonical name
of the encoding.
->renew
Predefined As:
sub renew {
my $self = shift;
my $clone = bless { %$self } => ref($self);
$clone->{renewed}++;
return $clone;
}
This method reconstructs the encoding object if neces-
sary. If you need to store the state during encoding,
this is where you clone your object.
PerlIO ALWAYS calls this method to make sure it has
its own private encoding object.
->renewed
Predefined As:
sub renewed { $_[0]->{renewed} || 0 }
Tells whether the object is renewed (and how many
times). Some modules emit "Use of uninitialized value
in null operation" warning unless the value is numeric
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so return 0 for false.
->perlio_ok()
Predefined As:
sub perlio_ok {
eval{ require PerlIO::encoding };
return $@ ? 0 : 1;
}
If your encoding does not support PerlIO for some rea-
sons, just;
sub perlio_ok { 0 }
->needs_lines()
Predefined As:
sub needs_lines { 0 };
If your encoding can work with PerlIO but needs line
buffering, you MUST define this method so it returns
true. 7bit ISO-2022 encodings are one example that
needs this. When this method is missing, false is
assumed.
Example: Encode::ROT13
package Encode::ROT13;
use strict;
use base qw(Encode::Encoding);
__PACKAGE__->Define('rot13');
sub encode($$;$){
my ($obj, $str, $chk) = @_;
$str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
$_[1] = '' if $chk; # this is what in-place edit means
return $str;
}
# Jr pna or ynml yvxr guvf;
*decode = \&encode;
1;
Why the heck Encode API is different?
It should be noted that the $check behaviour is different
from the outer public API. The logic is that the
"unchecked" case is useful when the encoding is part of a
stream which may be reporting errors (e.g. STDERR). In
such cases, it is desirable to get everything through
somehow without causing additional errors which obscure
the original one. Also, the encoding is best placed to
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know what the correct replacement character is, so if that
is the desired behaviour then letting low level code do it
is the most efficient.
By contrast, if $check is true, the scheme above allows
the encoding to do as much as it can and tell the layer
above how much that was. What is lacking at present is a
mechanism to report what went wrong. The most likely
interface will be an additional method call to the object,
or perhaps (to avoid forcing per-stream objects on other-
wise stateless encodings) an additional parameter.
It is also highly desirable that encoding classes inherit
from "Encode::Encoding" as a base class. This allows that
class to define additional behaviour for all encoding
objects.
package Encode::MyEncoding;
use base qw(Encode::Encoding);
__PACKAGE__->Define(qw(myCanonical myAlias));
to create an object with "bless {Name => ...}, $class",
and call define_encoding. They inherit their "name"
method from "Encode::Encoding".
Compiled Encodings
For the sake of speed and efficiency, most of the encod-
ings are now supported via a compiled form: XS modules
generated from UCM files. Encode provides the enc2xs
tool to achieve that. Please see enc2xs for more details.
SEE ALSO
perlmod, enc2xs
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