Hi,

Consider Allocators, e.g.:

struct Mallocator
{
   enum usesGC = false;

   /// implement alloc, free, etc. @nogc
}

struct GCAllocator
{
  enum usesGC = true;

   /// implement alloc, free, etc. via the GC
}

Now I want to have the function attributes set depending on the allocator implementation

template AutoGC(ALLOCATOR) if (isAllocator!ALLOCATOR)
{
   static if (!ALLOCATOR.usesGC)
      AutoGC = pragma(attrib, @nogc);
   else
      AutoGC = pragma(attrib, none);
}

@AutoGC!ALLOCATOR void fun(ALLOCATOR)() if(isAllocator!ALLOCATOR)
{
   void* p = ALLOCATOR.alloc(1024);
   // do something with p
   ALLOCATOR.free(p);
}

So fun!Mallocator would be @nogc and fun!GCAllocator wouldn't be @nogc.

This is a contrived example. In reality I would use this with custom array, hash map and other container implementations so I could use them in @nogc territory by just switching out the allocator.

Is it possible to do something like this ?

On Friday, 4 June 2021 at 11:33:32 UTC, wjoe wrote:

If they are templates, just don't specify attributes and the compiler will infer them for you.

If they are not templates, you have to do a separate copy under version or static if.

On Friday, 4 June 2021 at 11:36:09 UTC, Adam D. Ruppe wrote:

That's good to know. Thanks :)
A separate copy is exactly what I wanted to avoid but since they are templates it's np.