forcing weak purity

[Alex Rønne Petersen]

On 23-05-2012 14:21, deadalnix wrote:
> 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.

I think you're missing an amusing point:

class C { this() pure {} }

C foo() pure
{
     return new C(); // can trigger a collection!
}

-- 
Alex Rønne Petersen
alex at lycus.org
http://lycus.org