Re: Coercions and custom type parameters

----- Original Message -----
From: Yuval Kogman <[email protected]>
Sent: Thu, 24 Jul 2008 23:27:11 +0300
Re: Re: Coercions and custom type parameters

> Declaring an attribute with a parameterized type:
>
> 	has foo => (
> 		isa => "ArrayRef[Foo]",
> 		coerce => 1,
> 	);
>
> has a specific behavior right now, it enables only the coercions on
> the type "ArrayRef[Foo]".
>


OK, I hadn't thought about it that way.  So, I can declare a subtype  
that looks parametrized, but it really isn't.

subtype 'ArrayRef[Int]' => as 'Str' => where { 1 };


>
> Custom parametrized types could still make sense though:
>
> 	MyCustomType[Foo]
>
> is a useful construct for custom container types, for functors, etc
> etc, so deep_coerce *is* a useful property to have
>

Wow, I didn't know that was possible either.  You guys have thought of  
everything...

So, this is my custom collection, which is parameterizable:

   subtype 'BigArrayRef' => as 'ArrayRef' => where { scalar(@$_) > 1 };

   has 'my_big_arrayref' => ( is => 'rw', isa => 'BigArrayRef[Int]' );


Now, I can also create a pseudo parameterizable subtype, that does  
something like this:

   subtype 'BigArrayRef[Int] => as 'ArrayRef' => where {
       my $ar = $_;
       return unless scalar( @$ar ) > 1;
       for ( @$ar ) {
         return unless m/^ \d+ $/x;
       }
       return 1;
   }

Well what does this mean now:

has 'my_new_big_arrayref' => ( is => 'rw', isa => 'BigArrayRef[Int][Int]' );

I think I've just confused myself.  I'm going to sit down and play  
with this some more...

Thanks,
Charles Alderman