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 "goto"s 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.
