2 ms·

> given that there isn’t even any clean way to specify interface expected by C++ template, all you have is type traits Concepts?

• xyzzyz 4y ago
  Ah, sorry, I was not up to speed with C++, it’s called concepts now. So, how do I specify, using concepts, that my template expects a type which has a field “.foo” of type int?
  • siknad 4y ago
    template<typename T> concept has_foo = requires(T x){ { x.foo } -> std::same_as<int>; }; template<has_foo T> int get_foo(T x){...} // or template<typename T> requires has_foo<T> void f(T x){...} // or even void f(has_foo auto x) {...}
    • BobbyJo 4y ago
      Does the above provide more safety/guarantees/something than just: type hasFoo interface { getfoo() int setfoo(int) } func f(hasFoo) {} ?
      • BenFrantzDale 4y ago
        I don’t know Go, but I think less in that concepts are syntax guarantees, not semantic guarantees. I suspect interfaces (assuming they are opt-in) are semantic guarantees. That said, I’ve never run into this distinction being a problem, and you could provide opt-in mechanisms in C++. Of course, the C++ interface has zero runtime cost.
      • throwaway894345 4y ago
        The equivalent Go would be something like: func f[T interface{.Foo}](T) {} Of course, this doesn't exist in Go, so we must do: func f[T interface{GetFoo(); SetFoo()}](T) {} And then define setters and getters on every type we want to use, including defining new types (with the commensurate setters/getters) for types that we don't own (i.e., if you import a struct from another package and it doesn't have setters and getters defined, you have to create a new type that implements those setters/getters).