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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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ext::Encode::lib:PerloPrograemxmte:r:sEnRceofdee::lib::Encode::Encoding(3p)


           * 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 { return $_[0] }

           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.  Here is an exam-
           ple:

             sub renew {
                 my $self = shift;
                 my $clone = bless { %$self } => ref($self);
                 $clone->{clone} = 1; # so the caller can see it
                 return $clone;
             }

           Since most encodings are stateless the default behav-
           ior is just return itself as shown above.

           PerlIO ALWAYS calls this method to make sure it has
           its own private encoding object.

       ->perlio_ok()
           Predefined As:



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ext::Encode::lib:PerloPrograemxmte:r:sEnRceofdee::lib::Encode::Encoding(3p)


             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
       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



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ext::Encode::lib:PerloPrograemxmte:r:sEnRceofdee::lib::Encode::Encoding(3p)


       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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