Encode::Encoding
Encode::Encoding(3) Perl Programmers Reference Guide 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 $check is is false then "encode" MUST make a "best effort" to
convert the string - for example, by using a replacement charac-
ter.
->decode($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 con-
verted part leaving it starting with the problem fragment. If
perlio_ok() is true, SHOULD becomes MUST.
* If $check is false then "decode" should make a "best effort" to
convert the string - for example by using Unicode's "\x{FFFD}" as
a replacement character.
If you want your encoding to work with encoding pragma, you should also
implement the method below.
->cat_decode($destination, $octets, $offset, $terminator [,$check])
MUST decode $octets with $offset and concatenate it to $destina-
tion. Decoding will terminate when $terminator (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 necessary. 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 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 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 encod-
ings 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 let-
ting 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 otherwise 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::Encod-
ing".
Compiled Encodings
For the sake of speed and efficiency, most of the encodings 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 v5.8.6 2001-09-21 Encode::Encoding(3)
