ext::Encode::lib:PerloProgrext::Encode::lib::Encode::Encoding(3p)NAMEEncode::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 imple-
mentation 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 con-
verted and modify $string in-place to remove the con-
verted part leaving it starting with the problem frag-
ment. 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,
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SHOULD becomes MUST.
* If $check is false then "decode" should make a "best
effort" to convert the string - for example by using
Unicode's "\x{FFFD}" as a replacement character.
If you want your encoding to work with encoding pragma, you
should also implement the method below.
[,$check])
->cat_decode($destination, $octets, $offset, $terminator
MUST decode $octets with $offset and concatenate it to
$destination. 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 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 }
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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 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"
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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::Encoding".
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
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