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=encoding utf8 | ||
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=head1 NAME | ||
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Object::Iterate - iterators for objects that know the next element | ||
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=head1 SYNOPSIS | ||
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use Object::Iterate qw(iterate igrep imap); | ||
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iterate {...} $object; | ||
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my @filtered = igrep {...} $object; | ||
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my @transformed = imap {...} $object; | ||
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=head1 DESCRIPTION | ||
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This module provides control structures to iterate through the | ||
elements of an object that cannot be represented as list of items all | ||
at once. Objects can represent a virtual collection that is beyond | ||
the reaches of foreach, map, and grep because they cannot turn | ||
themselves into a list. | ||
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If the object can return a next element, it can use this module. | ||
Iterate assumes that the object responds to C<__next__> with the next | ||
element, and to C<__more__> with TRUE or FALSE if more elements remain | ||
to be processed. The C<__init__> method is called before the first | ||
iteration (if it exists), and is silently skipped otherwise. The | ||
control structure continues until the C<__more__> method returns FALSE | ||
(which does not mean that it visited all of the elements but that the | ||
object has decided to stop iterating). At the end of all iterations | ||
(when C<__more__> returns false), C<Object::Iterate> calls | ||
C<__final__> if it exists, and skips it otherwise. | ||
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Each control structure sets C<$_> to the current element, just like | ||
foreach, map, and grep. | ||
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=head2 Mutable method names | ||
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You do not really have to use the C<__next__>, C<__more__>, | ||
C<__init__>, or C<__final__> names. They are just the defaults which | ||
<Object::Iterate> stores in the package variables C<$Next>, C<$More>, | ||
C<$Init>, and C<$Final> respectively. This module does not export | ||
these variables, so you need to use the full package specification to | ||
change them (I<i.e.> C<$Object::Iterate::Next>). If your object does | ||
not have the specified methods, the functions will die. You may want | ||
to wrap them in eval blocks. | ||
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Since this module uses package variables to store these methods names, | ||
the method names apply to every use of the functions no matter the | ||
object. You might want to local()-ise the variables for different | ||
objects. | ||
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Before any control structure does its job, it checks the object to see | ||
if it can respond to these two methods, whatever you decide to call | ||
them, so your object must know that it can respond to these methods. | ||
AUTOLOADed methods cannot work since the module cannot know if they | ||
exist. | ||
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=over 4 | ||
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=item iterate BLOCK, OBJECT | ||
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Applies BLOCK to each item returned by C<< OBJECT->__next__ >>. | ||
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iterate { print "$_\n" } $object; | ||
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This is the same thing as using a while loop, but C<iterate()> | ||
stays out of your way. | ||
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while( $object->__more__ ) { | ||
local $_ = $object->__next__; | ||
...BLOCK... | ||
} | ||
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=item igrep BLOCK, OBJECT | ||
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Applies BLOCK to each item returned by C<< OBJECT->__next__ >>, and | ||
returns all of the elements for which the BLOCK returns TRUE. | ||
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my $output = igrep { print "$_\n" } $object; | ||
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This is a grep for something that cannot be represented as a | ||
list at one time. | ||
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while( $object->__more__ ) { | ||
local $_ = $object->__next__; | ||
push @output, $_ if ...BLOCK...; | ||
} | ||
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=item imap BLOCK, OBJECT | ||
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Applies BLOCK to each item returned by C<< OBJECT->__next__ >>, and | ||
returns the combined lists that BLOCK returns for each of the | ||
elements. | ||
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my @output = imap { print "$_\n" } $object; | ||
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This is a map for something that cannot be represented as a | ||
list at one time. | ||
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while( $object->$More ) { | ||
local $_ = $object->__next__; | ||
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push @output, ...BLOCK...; | ||
} | ||
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=back | ||
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=head1 ERROR MESSAGES | ||
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=over 4 | ||
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=item iterate object has no C<__more__()> method at script line N | ||
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You need to provide the method to let C<Object::Iterate> determine if | ||
more elements are available. You don't have to call it C<__more__> if | ||
you change the value of C<$Object::Iterate::More>. | ||
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=item iterate object has no C<__next__()> method at script line N | ||
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You need to provide the method to let Object::Iterate fetch the next | ||
element. You don't have to call it C<__next__> if you change the | ||
value of C<$Object::Iterate::Next>. | ||
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=back | ||
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=head1 SOURCE AVAILABILITY | ||
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This module is on Github: | ||
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http://github.com/briandfoy/object-iterate | ||
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=head1 TO DO | ||
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* let the methods discover the method names per object. | ||
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=head1 CREDITS | ||
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Thanks to Slaven Rezic for adding C<__init__> support | ||
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=head1 AUTHOR | ||
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brian d foy, C<< <briandfoy@pobox.com> >>. | ||
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=head1 COPYRIGHT AND LICENSE | ||
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Copyright © 2002-2024, brian d foy <briandfoy@pobox.com>. All rights reserved. | ||
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This program is free software; you can redistribute it and/or modify | ||
it under the terms of the Artistic License 2.0. | ||
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=cut | ||
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1; |