c++ - 静态重载与 SFINAE 结合使用

Question

我尝试在 Visual Studio 2013 中编译以下程序并得到了 C2686: cannot overload static and non-static member functions 错误。

#include <iostream>
#include <type_traits>

struct foo
{
  template<bool P>
  static std::enable_if_t<P> bar()
  {
    std::cerr << "P is true\n";
  }

  template<bool P>
  std::enable_if_t<!P> bar()
  {
    std::cerr << "P is false\n";
  }
};

int main()
{
  foo f;
  f.bar<true>();
}

我熟悉这个编译器错误 — 请参阅 this StackOverflow answer , 但惊讶地看到与 SFINAE 相关的错误，编译器将始终丢弃重载集中的两个重载之一。

Visual Studio 2013 是否正确遵循此处的标准，或者是否可以结合 SFINAE 在静态上重载？

编辑:将上面的示例与返回类型重载进行对比

如果没有 SFINAE，您将无法重载 static，也无法重载返回类型。但是，Visual Studio 2013 支持结合 SFINAE 重载返回类型。

以下程序与上面的程序相同，但删除了 static 并更改了第二个 foo::bar 声明的返回类型，编译正确。

#include <iostream>
#include <type_traits>

struct foo
{
  template<bool P>
  std::enable_if_t<P> bar()
  {
    std::cerr << "P is true\n";
  }

  template<bool P>
  std::enable_if_t<!P, int> bar()
  {
    std::cerr << "P is false\n";
    return 42;
  }
};

int main()
{
  foo f;
  f.bar<true>();
}

在我看来，Visual Studio 2013 将这两种情况中的一种弄错了，但我希望语言律师可以提供明确的答案。

Answer 1

令人惊讶的是，MSVC 是正确的。 (我知道，震惊。)[over.load]/p1-2:

1 Not all function declarations can be overloaded. Those that cannot be overloaded are specified here. A program is ill-formed if it contains two such non-overloadable declarations in the same scope. [Note: This restriction applies to explicit declarations in a scope, and between such declarations and declarations made through a using-declaration (7.3.3). It does not apply to sets of functions fabricated as a result of name lookup (e.g., because of using-directives) or overload resolution (e.g., for operator functions). —end note]

2 Certain function declarations cannot be overloaded:

• Function declarations that differ only in the return type cannot be overloaded.
• Member function declarations with the same name and the same parameter-type-list cannot be overloaded if any of them is a static member function declaration (9.4). Likewise, member function template declarations with the same name, the same parameter-type-list, and the same template parameter lists cannot be overloaded if any of them is a static member function template declaration. [...]
• [...]

两个bar()声明有相同的名字，相同的parameter-type-list，和相同的模板参数列表，至少其中一个是 static，因此不能重载。