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Encode::Encoding(3)   User Contributed Perl Documentation  Encode::Encoding(3)
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.
           o 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.
           o 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.
           o 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.
           o 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.
           o 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.
           o 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
perl v5.26.3                      2018-02-21               Encode::Encoding(3)