Encode::Encoding - man - phpman

NAME
    Encode::Encoding - Encode Implementation Base Class

SYNOPSIS
      package Encode::MyEncoding;
      use parent 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 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{
            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 {
            return eval { require PerlIO::encoding } ? 1 : 0;
          }

        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 parent 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 parent 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