C++11: How to alias a function? [duplicate]

Answer 1

It's not standard C++, but most compilers provide a way of doing this. With GCC you can do this:

void f () __attribute__ ((weak, alias ("__f")));

This creates the symbol f as an alias for __f. With VC++ you do the same thing this way:

#pragma comment(linker, "/export:f=__f")

Answer 2

The constexpr function pointer can be used as a function alias.

namespace bar
{
    int f();
}

constexpr auto g = bar::f;

It is highly likely (but not guaranteed by the language) that using g uses bar::f directly. Specifically, this depends on compiler version and optimization level.

In particular, this is the case for:

• GCC 4.7.1+, without optimization,
• Clang 3.1+, without optimization,
• MSVC 19.14+, with optimization.

See assembly generated by these compilers.

Answer 3

Classes are types, so they can be aliased with typedef and using (in C++11).

Functions are much more like objects, so there's no mechanism to alias them. At best you could use function pointers or function references:

void (*g)() = &bar::f;
void (&h)() = bar::f;

g();
h();

In the same vein, there's no mechanism for aliasing variables (short of through pointers or references).

Answer 4

You can define a function alias (with some work) using perfect forwarding:

template <typename... Args>
auto g(Args&&... args) -> decltype(f(std::forward<Args>(args)...)) {
  return f(std::forward<Args>(args)...);
}

This solution does apply even if f is overloaded and/or a function template.

Answer 5

Absolutely:

#include <iostream>

namespace Bar
{
   void test()
   {
      std::cout << "Test\n";
   }


   template<typename T>
   void test2(T const& a)
   {
      std::cout << "Test: " << a << std::endl;
   }
}

void (&alias)()        = Bar::test;
void (&a2)(int const&) = Bar::test2<int>;

int main()
{
    Bar::test();
    alias();
    a2(3);
}

Try:

> g++ a.cpp
> ./a.out
Test
Test
Test: 3
>

A reference is an alias to an existing object.
I just created a reference to a function. The reference can be used in exactly the same way as the original object.

Answer 6

It is possible to introduce the function into a different scope without changing its name. So you can alias a function with a different qualified name:

namespace bar {
  void f();
}

namespace baz {
  using bar::f;
}

void foo() {
  baz::f();
}