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 "\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 $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.

       ->mime_name
           Predefined As:

             sub mime_name{
               require Encode::MIME::Name;
               return Encode::MIME::Name::get_mime_name(shift->name);
             }

           MUST return the string representing the IANA charset 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 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 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