On 23-05-2012 15:55, deadalnix wrote:
Le 23/05/2012 15:47, Alex Rønne Petersen a écrit :
On 23-05-2012 15:46, deadalnix wrote:
Le 23/05/2012 14:32, Alex Rønne Petersen a écrit :
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!
}
Rethinking about this, it show something interesting. To make sense,
allocation in pure function should either be scoped or immutable.
Otherwise we can't ensure any « strong purity » on a function that
return anything that can reference something else.
Ok, but no direct call to GC collect will be done, so the function don't
need to be pure, it need to be somehow hacked into the allocation
mecanism, probably using compiler magic.
Sure there'll be a direct call to that. It's effectively what the GC
does when collecting.
At this point, you are in the allocation mecanism in druntime. You are
not in pure code anymore.
If it is the case, then the type system is broken at the wrong place.
The runtime is a bit of a special case in the first place. It's an
extremely low-level component of the language.
Mind you, I'm not saying there isn't room for improvement in our type
system!
--
Alex Rønne Petersen
[email protected]
http://lycus.org
