c++ - 检查两个函数或成员函数指针的签名是否相等

Question

我编写了一些代码来检查自由函数的签名是否等于成员函数的签名等。它比较提取的返回类型和函数参数:

#include <tuple>
#include <type_traits>

template<class Signature>
struct signature_trait;

template<class R, class... Args>
struct signature_trait<R(Args...)>
{
    using return_type = R;
    using arg_types = std::tuple<Args...>;
};

template<class R, class... Args>
struct signature_trait<R(*)(Args...)>
{
    using return_type = R;
    using arg_types = std::tuple<Args...>;
};

template<class R, class U, class... Args>
struct signature_trait<R(U::*)(Args...)>
{
    using return_type = R;
    using arg_types = std::tuple<Args...>;
};

template<class Signature>
using signature_trait_r = typename signature_trait<Signature>::return_type;

template<class Signature>
using signature_trait_a = typename signature_trait<Signature>::arg_types;

template<class Signature1, class Signature2>
using is_same_signature = 
    std::conjunction<
        std::is_same<signature_trait_r<Signature1>, signature_trait_r<Signature2>>, 
        std::is_same<signature_trait_a<Signature1>, signature_trait_a<Signature2>>
    >;

template<class Signature1, class Signature2>
inline constexpr bool is_same_signature_v = 
    is_same_signature<Signature1, Signature2>::value;

struct Foo
{
    void bar(int, int){}
};

void bar(int, int){}

int main()
{
    static_assert(is_same_signature_v<decltype(&bar), decltype(&Foo::bar)>, "");
    static_assert(is_same_signature_v<decltype(&bar), void(int, int)>, "");
    static_assert(is_same_signature_v<decltype(&Foo::bar), void(int, int)>, "");
    static_assert(is_same_signature_v<decltype(&Foo::bar), void(Foo::*)(int, int)>, "");
}

它工作得很好，但是可以简化吗？也许在某些情况下这个解决方案不起作用？

Answer 1

简单来说:没有理由分开return_type和arg_types :您可以将它们加入到一个 std::tuple 中与 return_type处于第一位置。

#include <tuple>
#include <type_traits>

template<class Signature>
struct signature_trait;

template<class R, class... Args>
struct signature_trait<R(Args...)>
 { using type = std::tuple<R, Args...>; };

template<class R, class... Args>
struct signature_trait<R(*)(Args...)>
 { using type = std::tuple<R, Args...>; };

template<class R, class U, class... Args>
struct signature_trait<R(U::*)(Args...)>
 { using type = std::tuple<R, Args...>; };

template<class Signature>
using signature_trait_t = typename signature_trait<Signature>::type;

template<class Signature1, class Signature2>
using is_same_signature = std::is_same<signature_trait_t<Signature1>,
                                       signature_trait_t<Signature2>>;

template<class Signature1, class Signature2>
inline constexpr bool is_same_signature_v = 
    is_same_signature<Signature1, Signature2>::value;

struct Foo
 { void bar (int, int) {} };

void bar (int, int) {}

int main ()
 {
    static_assert(is_same_signature_v<decltype(&bar), decltype(&Foo::bar)>, "");
    static_assert(is_same_signature_v<decltype(&bar), void(int, int)>, "");
    static_assert(is_same_signature_v<decltype(&Foo::bar), void(int, int)>, "");
    static_assert(is_same_signature_v<decltype(&Foo::bar), void(Foo::*)(int, int)>, "");
 }