Dan Sugalski <[EMAIL PROTECTED]> wrote:
> Right, for typed variables. Most variables (i.e. anything you
> declared with a plain "my $foo" or "our @bar") are untyped and can
> change their types as needed.
>
> If you did:
>
> my $foo;
> $foo = Dog.new();
> $foo = FireHydrant.new();
>
>
> $foo would first be a Dog, then a FireHydrant. When it changed to a
> FireHydrant the previous contents would get blown away.
Hmmm - how do we distinguish between a plain scalar that is temporarily
typed, and a 'proper' permanently-typed scalar?
eg in the following
my Dog $spot = Dog.new("waggly tail");
$spot = Cat.new();
you would expect $spot to always remain a dog no matter what, and will
throw a run-time (or compile time) error if it can't think of a way of
making itself into a "doggish" cat.
On the other hand,
my Dog $spot = Dog.new("waggly tail");
my $plain = 1;
$plain = $dog; # is $plain temporarily or permanently a dog now?
$plain = Cat.new(); # run-time error or is $plain now a cat?
Or to put it another way, is the type of a PMC determined purely by
it's current vtable pointer, and if so, under what circumstances
are we allowed to change the pointer? Do we need a PMC flag saying
that our type is fixed? And if so, how do we handle
my Dog $dog; # dog has the 'undef' vtable pointer type
# but is still a dog
$dog = Dog.new(); # dog now has the 'dog' vtable type.
And can we indeed conflate the concepts of type as defined by a vtable
pointer, and Perl-level type? Will there always be a seaprate vtable
for each Perl-level type????
I'm confused....
