MirOS Manual: Encode::Encoding(3p)


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 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.

     ->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.

     ->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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