Vincent Pit > with > with

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Module Version: 0.02   Source  

NAME ^

with - Lexically call methods with a default object.

VERSION ^

Version 0.02

SYNOPSIS ^

    package Deuce;

    sub new { my $class = shift; bless { id = > shift }, $class }

    sub hlagh { my $self = shift; print "Deuce::hlagh $self->{id}\n" }


    package Pants;

    sub hlagh { print "Pants::hlagh\n" }

    our @ISA;
    push @ISA, 'Deuce';
    my $deuce = new Deuce 1;

    hlagh;         # Pants::hlagh

    {
     use with \$deuce;
     hlagh;        # Deuce::hlagh 1
     Pants::hlagh; # Pants::hlagh
 
     {
      use with \Deuce->new(2);
      hlagh;       # Deuce::hlagh 2
     }

     hlagh;        # Deuce::hlagh 1

     no with;
     hlagh;        # Pants::hlagh
    }

    hlagh;         # Pants::hlagh

DESCRIPTION ^

This pragma lets you define a default object against with methods will be called in the current scope when possible. It is enabled by the use with \$obj idiom (note that you must pass a reference to the object). If you use with several times in the current scope, the default object will be the last specified one.

HOW DOES IT WORK ^

The main problem to address is that lexical scoping and source modification can only occur at compile time, while object creation and method resolution happen at run-time.

The use with \$obj statement stores an address to the variable $obj in the with field of the hints hash %^H. It also starts a source filter that replaces function calls with calls to with::defer, passing the name of the original function as the first argument. When the replaced function has a prototype or is part of the core, the call is deferred to a corresponding wrapper generated in the with namespace. Some keywords that couldn't possibly be replaced are also completely skipped. no with undefines the hint and deletes the source filter, stopping any subsequent modification in the current scope.

When the script is executed, deferred calls first fetch the default object back from the address stored into the hint. If the object ->can the original function name, a method call is issued. If not, the calling namespace is inspected for a subroutine with the proper name, and if it's present the program gotos into it. If that fails too, the core function with the same name is recalled if possible, or an "Undefined subroutine" error is thrown.

IGNORED KEYWORDS ^

A call will never be dispatched to a method whose name is one of :

    my our local sub do eval goto return
    if else elsif unless given when or and 
    while until for foreach next redo last continue
    eq ne lt gt le ge cmp
    map grep system exec sort print say
    new
    STDIN STDOUT STDERR

EXPORT ^

No function or constant is exported by this pragma.

CAVEATS ^

Most likely slow. Almost surely non thread-safe. Contains source filters, hence brittle. Messes with the dreadful prototypes. Crazy. Will have bugs.

Don't put anything on the same line of use with \$obj or no with.

When there's a function in the caller namespace that has a core function name, and when no method with the same name is present, the ambiguity is resolved in favor of the caller namespace. That's different from the usual perl semantics where sub push; push @a, 1 gets resolved to CORE::push.

If a method has the same name as a prototyped function in the caller namespace, and if a called is deferred to the method, it will have its arguments passed by value.

DEPENDENCIES ^

perl 5.9.4.

Carp (core module since perl 5).

Filter::Util::Call, Scalar::Util and Text::Balanced (core since 5.7.3).

Sub::Prototype::Util 0.08.

AUTHOR ^

Vincent Pit, <perl at profvince.com>, http://www.profvince.com.

You can contact me by mail or on #perl @ FreeNode (vincent or Prof_Vince).

BUGS ^

Please report any bugs or feature requests to bug-with at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=with. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc with

ACKNOWLEDGEMENTS ^

A fair part of this module is widely inspired from Filter::Simple (especially FILTER_ONLY), but a complete integration was needed in order to add hints support and more placeholder patterns.

COPYRIGHT & LICENSE ^

Copyright 2008 Vincent Pit, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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