encode::encoding(3)

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.

· If $check is false then "decode" should make a "best

effort" to convert the string - for example by using
Unicode's "FFD}" as a replacement character.

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.

->new_sequence

Predefined As:

sub new_sequence { return $_[0] }

This is a placeholder for encodings with state. It
should return an object which implements this
interface. All current implementations return the
original object.

->perlio_ok()

Predefined As:

sub perlio_ok {

eval{ require PerlIO::encoding };
return $@ ? 0 : 1;

}

If your encoding does not support PerlIO for some
reasons, 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
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

perl v5.8.0 2002-06-01 Encode::Encoding(3)