Re: Boost.Function variant needed

From: jaakko.jarvi_at_[hidden]
Date: 2001-11-15 17:20:07

I'm jumping into this discussion in the midde, so sorry if I got
something wrong. Just a few details:

> 3) Bind/Lambda can just wrap ref(x) in their own internal ref-like
classes to 
> allow parameters to be ignored. 
> 
> I'm looking at "ref(x)" as essentially a directive that says "use a
reference 
> to x instead of copying it". Bind and Lambda have a particular view
of how 
> this should be done (by making it a function object that ignores its 
> arguments), 
ref(x) does not create a function object in lambda, it just wraps the
reference.

> 
> struct negate {
>   template<typename T> typeof(-T()) operator()(const T&) { return
-T; } 
> };
> 
> Now if I have an object "op" of type negate, and I have the Lambda
object 
> -_1, it seems wrong that op(a, b) is ill-formed whereas (-_1)(a, b)
is -a. We 
> shouldn't lose the arity constraint just because we're using Lambda.

(-_1)(a, b) fails at compile time in lambda, so the arity constraint
             is still there

As a side note:

(-_2)(a, b) works, argument a is discarded 

So the highest placeholder index determines the arity of the lambda 
functor.

Jaakko