Manually allocate delegate?

[userABCabc123 via Digitalmars-d-learn]

On Sunday, 12 July 2015 at 09:03:25 UTC, Tofu Ninja wrote:
> On Sunday, 12 July 2015 at 08:47:37 UTC, ketmar wrote:
>> On Sun, 12 Jul 2015 08:38:00 +0000, Tofu Ninja wrote:
>>
>>> Is it even possible?
>>
>> what do you mean?
>
> Sorry, thought the title was enough.
>
> The context for a delegate(assuming not a method delegate) is 
> allocated by the GC. Is there any way to allocate the context 
> manually.

Yes:

========================
class Foo
{
     void bar(){writeln(__PRETTY_FUNCTION__);}
}

auto uncollectedDelegate(T, string name)(ref T t)
{
     import std.experimental.allocator.mallocator;
     struct Dg{void* ptr, funcptr;}

     void* funcptr = &__traits(getMember, T, name);
     void* ptr = cast(void*)t;

     Dg* dg = cast(Dg*) Mallocator.instance.allocate(Dg.sizeof);
     dg.ptr = ptr;
     dg.funcptr = funcptr;
     return dg;
}

void main(string[] args)
{
     Foo foo = new Foo;
     auto dg = uncollectedDelegate!(Foo, "bar")(foo);
     auto tdg = cast(void delegate()*) dg;
     (*tdg)();
}
========================

with just a type __traits(getMember,...) on a delegate will only 
return the function address in the process image. so without the 
context ptr, just like a static or a global function. Later you 
set the context by hand, using a pointer to an instance.