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type_traits: type_list_index[_v]

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This commit is contained in:
Michele Caini
2022-05-02 10:58:11 +02:00
parent 14d213d13e
commit 03477ce400
3 changed files with 64 additions and 7 deletions
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1
docs/md/core.md
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@@ -762,6 +762,7 @@ Here is a (possibly incomplete) list of the functionalities that come with a
type list:
* `type_list_element[_t]` to get the N-th element of a type list.
* `type_list_index[_v]` to get the index of a given element of a type list.
* `type_list_cat[_t]` and a handy `operator+` to concatenate type lists.
* `type_list_unique[_t]` to remove duplicate types from a type list.
* `type_list_contains[_v]` to know if a type list contains a given type.

66
src/entt/core/type_traits.hpp
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@@ -121,22 +121,22 @@ struct type_list_element;
/**
* @brief Provides compile-time indexed access to the types of a type list.
* @tparam Index Index of the type to return.
* @tparam Type First type provided by the type list.
* @tparam First First type provided by the type list.
* @tparam Other Other types provided by the type list.
*/
template<std::size_t Index, typename Type, typename... Other>
struct type_list_element<Index, type_list<Type, Other...>>
template<std::size_t Index, typename First, typename... Other>
struct type_list_element<Index, type_list<First, Other...>>
: type_list_element<Index - 1u, type_list<Other...>> {};
/**
* @brief Provides compile-time indexed access to the types of a type list.
* @tparam Type First type provided by the type list.
* @tparam First First type provided by the type list.
* @tparam Other Other types provided by the type list.
*/
template<typename Type, typename... Other>
struct type_list_element<0u, type_list<Type, Other...>> {
template<typename First, typename... Other>
struct type_list_element<0u, type_list<First, Other...>> {
/*! @brief Searched type. */
using type = Type;
using type = First;
};
/**
@@ -147,6 +147,58 @@ struct type_list_element<0u, type_list<Type, Other...>> {
template<std::size_t Index, typename List>
using type_list_element_t = typename type_list_element<Index, List>::type;
/*! @brief Primary template isn't defined on purpose. */
template<typename, typename>
struct type_list_index;
/**
* @brief Provides compile-time type access to the types of a type list.
* @tparam Type Type to look for and for which to return the index.
* @tparam First First type provided by the type list.
* @tparam Other Other types provided by the type list.
*/
template<typename Type, typename First, typename... Other>
struct type_list_index<Type, type_list<First, Other...>> {
/*! @brief Unsigned integer type. */
using value_type = std::size_t;
/*! @brief Compile-time position of the given type in the sublist. */
static constexpr value_type value = 1u + type_list_index<Type, type_list<Other...>>::value;
};
/**
* @brief Provides compile-time type access to the types of a type list.
* @tparam Type Type to look for and for which to return the index.
* @tparam Other Other types provided by the type list.
*/
template<typename Type, typename... Other>
struct type_list_index<Type, type_list<Type, Other...>> {
static_assert(type_list_index<Type, type_list<Other...>>::value == sizeof...(Other), "Non-unique type");
/*! @brief Unsigned integer type. */
using value_type = std::size_t;
/*! @brief Compile-time position of the given type in the sublist. */
static constexpr value_type value = 0u;
};
/**
* @brief Provides compile-time type access to the types of a type list.
* @tparam Type Type to look for and for which to return the index.
*/
template<typename Type>
struct type_list_index<Type, type_list<>> {
/*! @brief Unsigned integer type. */
using value_type = std::size_t;
/*! @brief Compile-time position of the given type in the sublist. */
static constexpr value_type value = 0u;
};
/**
* @brief Helper variable template.
* @tparam List Type list.
* @tparam Type Type to look for and for which to return the index.
*/
template<typename Type, typename List>
inline constexpr std::size_t type_list_index_v = type_list_index<Type, List>::value;
/**
* @brief Concatenates multiple type lists.
* @tparam Type Types provided by the first type list.

4
test/entt/core/type_traits.cpp
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@@ -78,6 +78,10 @@ TEST(TypeList, Functionalities) {
static_assert(std::is_same_v<entt::type_list_element_t<1u, type>, char>);
static_assert(std::is_same_v<entt::type_list_element_t<0u, other>, double>);
static_assert(entt::type_list_index_v<int, type> == 0u);
static_assert(entt::type_list_index_v<char, type> == 1u);
static_assert(entt::type_list_index_v<double, other> == 0u);
static_assert(std::is_same_v<entt::type_list_diff_t<entt::type_list<int, char, double>, entt::type_list<float, bool>>, entt::type_list<int, char, double>>);
static_assert(std::is_same_v<entt::type_list_diff_t<entt::type_list<int, char, double>, entt::type_list<int, char, double>>, entt::type_list<>>);
static_assert(std::is_same_v<entt::type_list_diff_t<entt::type_list<int, char, double>, entt::type_list<int, char>>, entt::type_list<double>>);