From D struct to C struct

[Namespace]

On Sunday, 17 November 2013 at 22:25:54 UTC, qznc wrote:
> On Sunday, 17 November 2013 at 22:11:02 UTC, Namespace wrote:
>> Hello.
>> I have some trouble with C interfacing.
>> I have a C struct with an integer member and I want to wrap 
>> this into a D template. But if I want to access the C API, I 
>> have to convert the C struct with the type informations of the 
>> D struct.
>> Example: http://dpaste.dzfl.pl/e3d10755
>>
>> The question is: How can I write the ptr method? It is very 
>> probable, that these conversion is often used, so the ptr 
>> method should be fast and without many garbage. And If 
>> possible, I want to avoid the GC / Heap.
>> My current approach doesn't avoid the GC complete, but it 
>> displace the problem: http://dpaste.dzfl.pl/449f663f
>>
>> Any further ideas how to solve that?
>
> You cannot use the stack due to your API requirements, so only 
> heap or data segment remains. I assume you cannot use static 
> variables, so heap it is. You should look into Andreis proposed 
> std.allocator to optimize your memory management.
>
> http://forum.dlang.org/post/l4btsk$5u8$1@digitalmars.com

I use my own allocators until Andreis are official merged into 
phobos.
But I hoped to avoid the Heap.

I found one solution which would work without using the heap, but 
I'm unsure how good and safe it is:

----
import std.stdio;

struct C {
	int id;
}

struct C2 {
	C _c = void;
	
	inout(C*) ptr() inout pure nothrow {
		return &this._c;
	}
}

struct D(T) {
	T id = 0;

	C2 asC2() const {
		return C2(C(cast(int) this.id));
	}

	/// Lots of more comfortable methods.
}

void stuff(const C* a, C* b) {
	writefln("a id = %d", a.id);
	writefln("b id = %d", b.id);
}

alias Df = D!float;

void main() {
	Df src;
	Df dst;

	stuff(src.asC2().ptr, dst.asC2().ptr);
}
----