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.\" ========================================================================
.\"
.IX Title "Dispatch::Class 3pm"
.TH Dispatch::Class 3pm "2022-10-15" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Dispatch::Class \- dispatch on the type (class) of an argument
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 4
\&  use Dispatch::Class qw(
\&    class_case
\&    dispatch
\&  );
\&  
\&  # analyze the class of an object
\&  my $analyze = class_case(
\&    \*(AqSome::Class\*(Aq  => 1,
\&    \*(AqOther::Class\*(Aq => 2,
\&    \*(AqUNIVERSAL\*(Aq    => "???",
\&  );
\&  my $foo = $analyze\->(Other::Class\->new);  # 2
\&  my $bar = $analyze\->(IO::Handle\->new);    # "???"
\&  my $baz = $analyze\->(["not an object"]);  # undef
\&
\&  # build a dispatcher
\&  my $dispatch = dispatch(
\&    \*(AqDog::Tiny\*(Aq => sub { ... },  # handle objects of the class Dog::Tiny
\&    \*(AqDog\*(Aq       => sub { ... },
\&    \*(AqMammal\*(Aq    => sub { ... },
\&    \*(AqTree\*(Aq      => sub { ... },
\&  
\&    \*(AqARRAY\*(Aq     => sub { ... },  # handle array refs
\&  
\&    \*(Aq:str\*(Aq      => sub { ... },  # handle non\-reference strings
\&  
\&    \*(Aq*\*(Aq         => sub { ... },  # handle any value
\&  );
\&  
\&  # call the appropriate handler, passing $obj as an argument
\&  my $result = $dispatch\->($obj);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module offers a (mostly) simple way to check the class of an object and
handle specific cases specially.
.SS "Functions"
.IX Subsection "Functions"
The following functions are available and can be imported on request:
.ie n .IP """class_case""" 4
.el .IP "\f(CWclass_case\fR" 4
.IX Item "class_case"
\&\f(CW\*(C`class_case\*(C'\fR takes a list of \f(CW\*(C`KEY, VALUE\*(C'\fR pairs and returns a code reference
that (when called on an object) will analyze the object's class according to
the rules described below and return the corresponding \fI\s-1VALUE\s0\fR of the first
matching \fI\s-1KEY\s0\fR.
.Sp
Example:
.Sp
.Vb 6
\&  my $subref = class_case(
\&    KEY1 => VALUE1,
\&    KEY2 => VALUE2,
\&    ...
\&  );
\&  my $value = $subref\->($some_object);
.Ve
.Sp
This will check the class of \f(CW$some_object\fR against \f(CW\*(C`KEY1\*(C'\fR, \f(CW\*(C`KEY2\*(C'\fR, ... in
order and return the corresponding \f(CW\*(C`VALUEn\*(C'\fR of the first match. If no key
matches, an empty list/undef is returned in list/scalar context, respectively.
.Sp
The following things can be used as keys:
.RS 4
.ie n .IP """*""" 4
.el .IP "\f(CW*\fR" 4
.IX Item "*"
This will match any value. No actual check is performed.
.ie n .IP """:str""" 4
.el .IP "\f(CW:str\fR" 4
.IX Item ":str"
This special key will match any non-reference.
.ie n .IP """SCALAR"", ""ARRAY"", ""HASH"", ..." 4
.el .IP "\f(CWSCALAR\fR, \f(CWARRAY\fR, \f(CWHASH\fR, ..." 4
.IX Item "SCALAR, ARRAY, HASH, ..."
These values match references of the specified type even if they aren't objects
(i.e. not \f(CW\*(C`bless\*(C'\fRed). That is, for unblessed references the
string returned by \f(CW\*(C`ref\*(C'\fR is compared with
\&\f(CW\*(C`eq\*(C'\fR.
.IP "\s-1CLASS\s0" 4
.IX Item "CLASS"
Any other string is interpreted as a class name and matches if the input value
is an object for which \f(CW\*(C`$obj\->isa($CLASS)\*(C'\fR is true. To match any kind of
object (blessed value), use the key \f(CW\*(AqUNIVERSAL\*(Aq\fR.
.Sp
Starting with Perl 5.10.0 Perl supports
checking for roles with \f(CW\*(C`DOES\*(C'\fR, so
\&\f(CW\*(C`Dispatch::Class\*(C'\fR actually uses \f(CW\*(C`$obj\->DOES($CLASS)\*(C'\fR instead of \f(CW\*(C`isa\*(C'\fR.
This still returns true for normal base classes but it also accepts roles that
have been composed into the object's class.
.RE
.RS 4
.RE
.ie n .IP """dispatch""" 4
.el .IP "\f(CWdispatch\fR" 4
.IX Item "dispatch"
This works like \f(CW\*(C`class_case\*(C'\fR above, but the \fI\s-1VALUE\s0\fRs must be code references
and get invoked automatically:
.Sp
.Vb 8
\&  sub dispatch {
\&    my $analyze = class_case @_;
\&    sub {
\&      my ($obj) = @_;
\&      my $handler = $analyze\->($obj) or return;
\&      $handler\->($obj)
\&    }
\&  }
.Ve
.Sp
That is, the matching object is passed on to the matched \fI\s-1VALUE\s0\fRs and the
return value of the inner sub is whatever the handler returns (or the empty
list/undef if no \fI\s-1KEY\s0\fR matches).
.PP
This module uses \f(CW\*(C`Exporter::Tiny\*(C'\fR, so you can rename the
imported functions at \f(CW\*(C`use\*(C'\fR time.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Exporter::Tiny
.SH "AUTHOR"
.IX Header "AUTHOR"
Lukas Mai, \f(CW\*(C`<l.mai at web.de>\*(C'\fR
.SH "COPYRIGHT & LICENSE"
.IX Header "COPYRIGHT & LICENSE"
Copyright 2013, 2014 Lukas Mai.
.PP
This program is free software; you can redistribute it and/or modify it
under the terms of either: the \s-1GNU\s0 General Public License as published
by the Free Software Foundation; or the Artistic License.
.PP
See http://dev.perl.org/licenses/ for more information.