Re^3: Griping about Typing

[tadman]

in reply to Re: Re: Griping about Typing
in thread Griping about Typing

Okay, can anyone explain how that works? It actually parses, though the class is completely ignored, provided it is defined somewhere. Here's a quick example:

#!/usr/bin/perl -w

use strict;
use CGI;
use LWP;

my CGI $cgi = new CGI();      # Works
my XYZ $cgi = new CGI();      # "No such class XYZ ..."
my LWP $cgi = new CGI();      # Works, strangely enough

Nothing in the docs about that, at least under my.

[pdcawley]

It isn't quite ignored, but it only really does anything if you're using pseudo hashes and you've defined your the class using use fields, in which case, $CGI would be initialized as an arrayref with an appropriate hashref in the zeroth slot.

[Anonymous Monk]

Perl records this information, but does nothing (or very little) with it. Because it is recorded, the typesafety.pm and types.pm modules are able to use it. This kind of core hooks for extensibility via modules is a recurring pattern in Perl: overload.pm can intercept the definitions of constants and turn them into objects; attributes.pm handles cases where tags like :foo appear after variables or sub definitions (in cases where the tag isn't one of the built ins like :lvalue, :method, or the depricated :shared). This feature, like attributes, went through growing pains. It is undocumented because it is still experimental - the details of how and when it is used are up in the air, even though some experimental modules are using it now.

The short of it is, use types.pm and/or typesafety.pm. http://perldesignpatterns.com/?TypeSafety has an intro to the idea of type safety and details about the Perl implementations. It quotes this thread heavily =) I hope this answers your question.

-scott