On Tuesday, December 16, 2003, at 12:20 PM, Gordon Henriksen wrote:
finally by default? None for me; thanks, though.
I don't think so; we're just talking about whether you can extend a class at _runtime_, not _compiletime_. Whether or not Perl can have some degree of confidence that, once a program is compiled, it won't have to assume the worst-case possibility of runtime alteration of every class, upon every single method call, just in case you've screwed with something.
They still aren't "final" classes, in that you can subclass them at will. You just can't subclass them _runtime_, via C<eval>, unless you've specifically marked that you want to allow that for that _specific_ class.
As Larry hypothesized:
The other reason for "final" is to make it easy for the compiler to optimize. That's also problematical. As implemented by Java, it's a premature optimization. The point at which you'd like to know this sort of thing is just after parsing the entire program and just before code generation. And the promises have to come from the users of interfaces, not the providers, because the providers don't know how their services are going to be used. Methods, roles, and classes may never declare themselves final. They may be declared final only by the agreement of all their users.
But the agreement could be implied by silence. If, by the time the entire program is parsed, nobody has said they want to extend an interface, then the interface can be considered closed. In other words, if you think you *might* want to extend an interface at run time, you'd better say so at compile time somehow. I think that's about as far as we can push it in the "final" direction.
-and-
Actually, I think making people declare what they want to extend might actually provide a nice little safety mechanism for what can be modified by the eval and what can't. It's not exactly Safe, but it's a little safer.
-and-
Seriously, I hope we can provide a framework in which you can screw around to your heart's content while modules are being compiled, and to a lesser extent after compilation. But we'll never get to a programming-in-the-large model if we can't limit most of the screwing around to the lexical scope currently being compiled, or at least to a known subset of the code.
So, if I may interpret that; it might not be so bad to have to declare whether or not you were going to extend/alter a class at runtime, in order that Perl could optimize what it knows at compile-time for the 99.5% of the classes that you wouldn't be doing that for.
MikeL
