forcing weak purity

[deadalnix]

Le 23/05/2012 05:22, Steven Schveighoffer a écrit :
> I have come across a dilemma.
>
> Alex Rønne Petersen has a pull request changing some things in the GC to
> pure. I think gc_collect() should be weak-pure, because it could
> technically run on any memory allocation (which is already allowed in
> pure functions), and it runs in a context that doesn't really affect
> execution of the pure function.
>
> So I think it should be able to be run inside a strong pure function.
> But because it has no parameters and no return, marking it as pure makes
> it strong pure, and an optimizing compiler can effectively remove the
> call completely!
>
> So how do we force something to be weak-pure? What I want is:
>
> 1. it can be called from a pure function
> 2. it will not be optimized out in any way.
>
> This solution looks crappy to me:
>
> void gc_collect(void *unused = null);
>
> any other ideas?
>
> -Steve

Why a pure function can call a collection cycle ???? This is an impure 
operation by essence.

I think what is need here is to break the type system to allow call of 
impure function into a pure one.