templates - SFINAE:检查两个可变参数包的串联是否与一个包相同

Question

有没有办法检查两个可变参数包的串联是否与第三个可变参数包相同。

template<typename... Args>
struct ClassOne
{
}

template<typename... Args>
struct ClassTwo
{
}

template<typename... Args>
struct ClassThree
{
}

template<typename... PackA, typename... PackB, typename... PackC>
void foo(ClassOne<PackA...>, ClassTwo<PackB...>, ClassThree<PackC...>)
{
}

我希望 foo 仅在 PackA... = PackB..., PackC... 时启用

Answer 1

比较直接...

template <typename ...>
struct pack{};

template<typename... PackA, typename... PackB, typename... PackC,
  typename = typename std::enable_if
     <std::is_same<pack<PackA...>, 
                   pack<PackB..., PackC...>>::value
     >::type>
void foo(ClassOne<PackA...>, ClassTwo<PackB...>, ClassThree<PackC...>)
{
}