我如何static_assert迭代器取消引用的类型？

Question

template <typename InputIterator>
MyFun(const InputIterator begin, const InputIterator end)
{
    // I want to static_assert that decltype(*begin) == SomeType
}

我该怎么做？我在想static_assert(std::is_same<*InputIterator,SomeType>)，但那当然不起作用......

Answer 1

std::iterator_traits：

static_assert(is_same<typename std::iterator_traits<InputIterator>::value_type, 
               SomeType>::value, "");

Answer 2

另一种使用decltype的替代方法，传递一个注释，它经常产生一个引用（但可能不会！）。

// If you want to assert that the dereferenced item is indeed a reference
static_assert(std::is_same<decltype(*begin), SomeType&>::value, "");

// If you are only interested in the "bare" type
// (equivalent to Jesse's providing iterator_traits was properly specialized)
static_assert(std::is_same<
    typename std::remove_reference<decltype(*begin)>::type,
    SomeType
>::value, "");