I've been hearing that delegates get a context pointer which will be allocated on the GC. Is this also true for delegates which stay in scope?

e.g.

void addThree() {
	int val;
	void addOne() {
		val++;
	}
	
	addOne();
	addOne();
	addOne();

	return val;
}

Will the above function allocate on the GC?

On Wed, 20 Aug 2014 10:44:38 -0400
Etienne via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

> Will the above function allocate on the GC?
no.

On Wed, 20 Aug 2014 10:44:38 -0400
Etienne via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
wrote:

and this is not delegate, this is just nested function.

On Wednesday, 20 August 2014 at 14:54:31 UTC, ketmar via Digitalmars-d-learn wrote:
> On Wed, 20 Aug 2014 10:44:38 -0400
> Etienne via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com>
> wrote:
>
> and this is not delegate, this is just nested function.

non-static nested functions are effectively delegates as it needs a context pointer to parent stack frame. However, not every delegate is a closure - heap allocation of the context happens only if delegate leaves the scope it refers to (via return value or by being passed as an argument to external function)

> non-static nested functions are effectively delegates as it needs a context pointer to parent stack frame.

Only if it is recursive.

On Wednesday, 20 August 2014 at 14:44:39 UTC, Etienne wrote:
> I've been hearing that delegates get a context pointer which will be allocated on the GC. Is this also true for delegates which stay in scope?
>
> e.g.
>
> void addThree() {
> 	int val;
> 	void addOne() {
> 		val++;
> 	}
> 	
> 	addOne();
> 	addOne();
> 	addOne();
>
> 	return val;
> }
>
> Will the above function allocate on the GC?

int getInt1() @nogc
{
	int val;
	int func() @nogc { return val; }
	return func();
}

int delegate() getInt2() //@nogc - thie one allocates!
{
	int val;
	int func() @nogc { return val; }
	return &func;
}

int delegate() getInt3() @nogc
{
	int val;
	int func() @nogc { return 0; }
	return &func;
}

On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr wrote:
>> non-static nested functions are effectively delegates as it needs a context pointer to parent stack frame.
>
> Only if it is recursive.

Or if it refers to any state of the parent function.

On Wednesday, 20 August 2014 at 20:48:38 UTC, Chris Nicholson-Sauls wrote:
> On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr wrote:
>>> non-static nested functions are effectively delegates as it needs a context pointer to parent stack frame.
>>
>> Only if it is recursive.
>
> Or if it refers to any state of the parent function.

As long as the compiler knows where it will be called from it should be able use a stack pointer offset (unless alloca gets in the way) without the frame pointer of the parent.

On Wednesday, 20 August 2014 at 21:19:18 UTC, Ola Fosheim Gr wrote:
> On Wednesday, 20 August 2014 at 20:48:38 UTC, Chris Nicholson-Sauls wrote:
>> On Wednesday, 20 August 2014 at 15:17:52 UTC, Ola Fosheim Gr wrote:
>>> Only if it is recursive.
>>
>> Or if it refers to any state of the parent function.
>
> As long as the compiler knows where it will be called from it should be able use a stack pointer offset (unless alloca gets in the way) without the frame pointer of the parent.

Well, I guess simple recursion could be solved easily too by having a wrapper function that puts the frame pointer in a free callee save register...

On 2014-08-20 5:25 PM, Ola Fosheim Gr wrote:
>
> Well, I guess simple recursion could be solved easily too by having a
> wrapper function that puts the frame pointer in a free callee save
> register...

So, my question inspired a new optimization? :-p