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types/traits: add inner_type query for ::value_type

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This commit is contained in:
Danny Robson 2018-03-12 23:11:26 +11:00
parent 5bc2cf12d4
commit 741012151b
1 changed files with 24 additions and 0 deletions
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24
types/traits.hpp
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@ -328,4 +328,28 @@ struct is_contiguous<std::vector<T,Allocator>>: public std::true_type {};
template <typename T>
constexpr auto is_contiguous_v = is_contiguous<T>::value;
///////////////////////////////////////////////////////////////////////////////
/// stores the type of '::value_type' for a given type, or the type itself if
/// it does not have such a type.
template <typename ValueT, typename = std::void_t<>>
struct inner_type {
using type = ValueT;
};
//-----------------------------------------------------------------------------
template <typename ValueT>
struct inner_type<
ValueT,
std::void_t<typename ValueT::value_type>
> {
using type = typename ValueT::value_type;
};
//-----------------------------------------------------------------------------
template <typename ValueT>
using inner_type_t = typename inner_type<ValueT>::type;
#endif