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.IX Title "File::Find::Rule::Extending 3"
.TH File::Find::Rule::Extending 3 2023-07-25 "perl v5.38.0" "User Contributed Perl Documentation"
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.SH NAME
File::Find::Rule::Extending \- the mini\-guide to extending File::Find::Rule
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 2
\& package File::Find::Rule::Random;
\& use strict;
\& 
\& # take useful things from File::Find::Rule
\& use base \*(AqFile::Find::Rule\*(Aq;
\&
\& # and force our crack into the main namespace
\& sub File::Find::Rule::random () {
\&     my $self = shift()\->_force_object;
\&     $self\->exec( sub { rand > 0.5 } );
\& }
\& 
\& 1;
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
File::Find::Rule went down so well with the buying public that
everyone wanted to add extra features.  With the 0.07 release this
became a possibility, using the following conventions.
.SS "Declare your package"
.IX Subsection "Declare your package"
.Vb 2
\& package File::Find::Rule::Random;
\& use strict;
.Ve
.SS "Inherit methods from File::Find::Rule"
.IX Subsection "Inherit methods from File::Find::Rule"
.Vb 2
\& # take useful things from File::Find::Rule
\& use base \*(AqFile::Find::Rule\*(Aq;
.Ve
.PP
\fIForce your madness into the main package\fR
.IX Subsection "Force your madness into the main package"
.PP
.Vb 5
\& # and force our crack into the main namespace
\& sub File::Find::Rule::random () {
\&     my $self = shift()\->_force_object;
\&     $self\->exec( sub { rand > 0.5 } );
\& }
.Ve
.PP
Yes, we're being very cavalier here and defining things into the main
File::Find::Rule namespace.  This is due to lack of imaginiation on my
part \- I simply can't find a way for the functional and oo interface
to work without doing this or some kind of inheritance, and
inheritance stops you using two File::Find::Rule::Foo modules
together.
.PP
For this reason try and pick distinct names for your extensions.  If
this becomes a problem then I may institute a semi-official registry
of taken names.
.SS "Taking no arguments."
.IX Subsection "Taking no arguments."
Note the null prototype on random.  This is a cheat for the procedural
interface to know that your sub takes no arguments, and so allows this
to happen:
.PP
.Vb 1
\& find( random => in => \*(Aq.\*(Aq );
.Ve
.PP
If you hadn't declared \f(CW\*(C`random\*(C'\fR with a null prototype it would have
consumed \f(CW\*(C`in\*(C'\fR as a parameter to it, then got all confused as it
doesn't know about a \f(CW\*(Aq.\*(Aq\fR rule.
.SH AUTHOR
.IX Header "AUTHOR"
Richard Clamp <richardc@unixbeard.net>
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright (C) 2002 Richard Clamp.  All Rights Reserved.
.PP
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
File::Find::Rule
.PP
File::Find::Rule::MMagic was the first extension module, so maybe
check that out.