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Re: Will subroutine signatures apply to methods in Perl6

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From:
Piers Cawley
Date:
August 25, 2001 03:22
Subject:
Re: Will subroutine signatures apply to methods in Perl6
Message ID:
m3pu9kv3sx.fsf@iest.bofh.org.uk
"Brent Dax" <brentdax@cpan.org> writes:
> # From: Uri Guttman [mailto:uri@sysarch.com]
> #   BD> equivalent) in method lookups?  In other words, if
> # $spot is declared to
> #   BD> hold a Dog, can we assume that it does, thus skipping
> # the check with
> #   BD> 'ref' normally used for method dispatch?  Would this even buy us
> #   BD> anything?  Why am I asking myself these questions?  Why are the
> #   BD> orderlies putting me in a white truck?
> #
> # no, that won't work. you can always bypass that at runtime in too many
> # ways. as damian stated, runtime checks for objects are always in
> # effect. if a method isn't found or handled by AUTOLOAD or something it
> # is fatal (unless caught, of course). the method itself will
> # always need
> # to check its arguments if it cares about whether a class or object is
> # the invocant (i like that word. thanx, damian!).
> 
> I'm not sure if you understood what I meant there.  I meant that, if we
> know $spot is supposed to have a Dog in it, can we avoid checking if it
> really does (at least some of the time) and maybe shuck some overhead by
> doing so?  Perhaps we only check after each assignment to $spot, and
> when we check we set a flag saying that it's already been typechecked so
> we don't have to do it again.  Whatever, methinks I may optimizing too
> early.  We all know what Knuth says about that.

You missed out another checking possibility:


    sub Foo::method { bless $_[1], 'Bar' }

    my Dog $spot = Dog.new(type => 'Poodle');

    Foo->method($spot);

Unless I've totally misunderstood the current proposals for what
happens with arguments passed in, it's still going to be possible to
rebless an argument, therefore $spot will need to be rechecked after
every method call to which it is passed as an argument.

-- 
Piers Cawley
www.iterative-software.com


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