Re: The value of declarations

[moritz]

I share your love for strict and declarations, and I'm pleased that Perl 6 has strict mode enabled by default (except for one-liners).

It also comes with very expressive signatures, different declarations for subs and methods (which also improves introspection) and all sorts of other things you can expect from a modern programming languages. Heck, even sub names will be checked at compile time (actually at CHECK time, iirc) and you'll get very friendly error messages.

[TimToady]

The one place where the design of Perl 6 doesn't quite jibe with this meditation is that, while Perl 6 can do compile-time checking of named arguments on subroutines, it refuses to do so for method calls. (It does this by supplying a default slurpy %_ parameter to methods.) The reasoning for this is that base methods should be allowed to ignore named parameters that are intended only for derived methods, and vice versa. Perhaps there is some way to check named arguments against all the candidates at run time, but it seems as though this could get expensive, and we're at least trying to maintain the hope that Perl 6 could be very fast in theory, even if 6.0.0 doesn't actually achieve that. (And we don't expect it to, since we're optimizing for correct over fast for now.) Anyway, we're still open to ideas in this area, maybe an optional check that only runs first time when dispatch order is established (or reestablished).

[moritz]

I wonder, can you do any reliable compile time checks on methods at all? I think this is valid:

my $x = eval 'class A { method foo($bar, $baz} }; A.new';
$x.foo();

Any compile time check would complain about a missing method.

[TGI]

Some checks could be done if you had a way to tell the compiler you weren't going to do something like this.

__PACKAGE__->no_monkey_business;  # no new methods/method signatures c
+an happen now. 

# or perhaps

use static_methods qw( MyClass );  #compile this class with only expli
+citly declared methods allowed.

Where the declaration says that only the methods that exist for the class at that time, or perhaps those that have been explicitly declared are available.

Even better if you could turn it off from outside the class file, so you could do some monkey patching if needed:

# in main:
no static_methods MyClass;  # uses MyClass with static_methods turned 
+off.