Encode::Encoding(3p) Perl Programmers Reference Guide Encode::Encoding(3p) #
Encode::Encoding(3p) Perl Programmers Reference Guide Encode::Encoding(3p)
NNAAMMEE #
Encode::Encoding - Encode Implementation Base Class
SSYYNNOOPPSSIISS #
package Encode::MyEncoding;
use parent qw(Encode::Encoding);
__PACKAGE__->Define(qw(myCanonical myAlias));
DDEESSCCRRIIPPTTIIOONN #
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
eennccooddee(()) and ddeeccooddee(()) methods.
MMeetthhooddss yyoouu sshhoouulldd iimmpplleemmeenntt You are strongly encouraged to implement methods below, at least either eennccooddee(()) or ddeeccooddee(()).
->encode($string [,$check])
MUST return the octet sequence representing _$_s_t_r_i_n_g.
• If _$_c_h_e_c_k is true, it SHOULD modify _$_s_t_r_i_n_g in place to remove the
converted part (i.e. the whole string unless there is an error).
If ppeerrlliioo__ookk(()) 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 $string in-
place to remove the converted part leaving it starting with the
problem fragment. If ppeerrlliioo__ookk(()) is true, SHOULD becomes MUST.
• If _$_c_h_e_c_k 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 _$_o_c_t_e_t_s represents.
• If _$_c_h_e_c_k is true, it SHOULD modify _$_o_c_t_e_t_s in place to remove the
converted part (i.e. the whole sequence unless there is an error).
If ppeerrlliioo__ookk(()) is true, SHOULD becomes MUST.
• If an error occurs, it SHOULD return the fragment of string that
has been converted and modify $octets in-place to remove the
converted part leaving it starting with the problem fragment. If
ppeerrlliioo__ookk(()) is true, SHOULD becomes MUST.
• If _$_c_h_e_c_k 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 _$_o_c_t_e_t_s with _$_o_f_f_s_e_t and concatenate it to _$_d_e_s_t_i_n_a_t_i_o_n.
Decoding will terminate when $terminator (a string) appears in
output. _$_o_f_f_s_e_t will be modified to the last $octets position at end
of decode. Returns true if $terminator appears output, else returns
false.
OOtthheerr mmeetthhooddss ddeeffiinneedd iinn EEnnccooddee::::EEnnccooddiinnggss 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.
->ppeerrlliioo__ookk(())
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 }
->nneeeeddss__lliinneess(())
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.
EExxaammppllee:: EEnnccooddee::::RROOTT1133 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 $str;
}
# Jr pna or ynml yvxr guvf;
*decode = \&encode;
1;
WWhhyy tthhee hheecckk EEnnccooddee AAPPII iiss ddiiffffeerreenntt?? It should be noted that the _$_c_h_e_c_k 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 _$_c_h_e_c_k 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".
CCoommppiilleedd EEnnccooddiinnggss For the sake of speed and efficiency, most of the encodings are now supported via a _c_o_m_p_i_l_e_d _f_o_r_m: XS modules generated from UCM files. Encode provides the enc2xs tool to achieve that. Please see enc2xs for more details.
SSEEEE AALLSSOO #
perlmod, enc2xs
perl v5.36.3 2019-02-13 Encode::Encoding(3p)