Overriding a [[noreturn]] virtual function

Question

The [[noreturn]] attribute can be applied to functions that are not meant to return. For example:

[[noreturn]] void will_throw() { throw std::r         


        

Answer 1

In practice, neither g++, clang nor MSVC consider the [[noreturn]] attribute as inherited

#include <iostream>

struct B {
public:
  [[noreturn]] virtual void f() { std::cout << "B\n"; throw 0; }
};

struct D : public B {
  void f() override { std::cout << "D\n"; }
};

int main() 
{
    try { B{}.f(); } catch(...) {}
    D{}.f();

    B* d = new D{};
    d->f();
}

which prints out "B", "D" and "D" for all three compilers.

Answer 2

Consider what you are actually saying:

class B
{
public:
    [[noreturn]] virtual void f() { throw std::runtime_error(""); }
};

Certainly the human reader, and possibly the compiler, would interpret this as a 'contract', i.e.
"f() wont return, I promise"

That should then apply to overrides of f() too, or else you are breaking the contract.

The standard might be underspecified on this, but even if it works, I would recommend against it based on readability.

Answer 3

I have grepped through the standard, and there's no indication that either [[noreturn]] specifically, or attributes more generally, are "inherited" by overriding functions.

It's hard to prove a negative, and the standard actually doesn't declare this either way but, since A::f() and B::f() are still distinct functions and the only behaviour described is defined in terms of functions, I think you're safe to mark A::f() as [[noreturn]].

That being said, I can't imagine what useful optimisation the compiler could subsequently perform, given the dynamic dispatch.