I'd like to reinterpret data as different type without copying.

extern(C) struct A{ /* */ }
struct B
{
  A a;
  alias a this;
}

extern(C) A* f1(){ /* */ }

B* f2()
{
  return cast(B*) f1();
}

Assuming that i cast() correct state, i'd like to know if:
* it's currently safe
* it's guaranteed to be safe in the future
* there any precautions in using this pattern

Most important thing for me is a type-check, but defining operators ( since they can't be external ) would be nice too.

I'm asking because i'd like to use this pattern a lot in my code, and with my limited knowledge it's good to get some feedback of more experienced.

Ps.
  In situations when i return by value instead of pointer - will memory copying be optimized away ?

Mariusz `shd` Gliwiński:

> * it's currently safe

One thing to remember when casting, is that when you cast const/immutable to mutable, then you can't mutate the data.

Bye,
bearophile