Traits: add is_pairish_of_v type trait

The trait allows to check if the type is a pair-like object, containing
objects of two particular types.

src/Utils/Traits.hpp

@@ -58,6 +58,7 @@
  * tuple_iseq
  * is_tuplish_v (standard (tuple, array, pair) + bounded array)
  * is_pairish_v
+ * is_pairish_of_v
  * is_tuplish_of_pairish_v
  * is_variant_v
  * is_optional_v
@@ -489,6 +490,24 @@ struct is_pairish_h<T, std::void_t<
 template <class T>
 constexpr bool is_pairish_v = details::is_pairish_h<std::remove_cv_t<T>>::value;
 
+namespace details {
+template <class T, class V1, class V2, class _ = void>
+struct is_pairish_of_h : std::false_type {};
+
+template <class T, class V1, class V2>
+struct is_pairish_of_h<T, V1, V2, std::void_t<
+	std::enable_if_t<is_pairish_v<T>, void>,
+	std::enable_if_t<std::is_same_v<std::remove_cv_t<decltype(std::declval<T&>().first)>, V1>, void>,
+	std::enable_if_t<std::is_same_v<std::remove_cv_t<decltype(std::declval<T&>().second)>, V2>, void>>>
+: std::true_type {};
+} //namespace details {
+
+template <class T, class V1, class V2>
+constexpr bool is_pairish_of_v = details::is_pairish_of_h<
+	std::remove_cv_t<T>,
+	std::remove_cv_t<V1>,
+	std::remove_cv_t<V2>>::value;
+
 /**
  * Check whether the type is compatible with std::tuple (see is_tuplish_v) and
  * consist of types that are compatible with std::pair (see is_pairish_v).

test/TraitsUnitTest.cpp

@@ -582,6 +582,24 @@ test_tuple_pair_traits()
 	static_assert(!tnt::is_pairish_v<Test>);
 	static_assert(!tnt::is_pairish_v<const_int>);
 
+	static_assert(tnt::is_pairish_of_v<std::pair<int, bool>, int, bool>);
+	static_assert(!tnt::is_pairish_of_v<std::pair<int, bool>, bool, int>);
+	static_assert(!tnt::is_pairish_of_v<std::pair<int, bool>, int, char>);
+	static_assert(!tnt::is_pairish_of_v<std::pair<int, bool>, char, bool>);
+	static_assert(tnt::is_pairish_of_v<const volatile std::pair<int, int>, int, int>);
+	static_assert(tnt::is_pairish_of_v<std::pair<int&, float&&>, int&, float&&>);
+	static_assert(!tnt::is_pairish_of_v<const std::pair<int, int>&, int, int>);
+	static_assert(tnt::is_pairish_of_v<CustomPair, int, double>);
+	static_assert(tnt::is_pairish_of_v<const CustomPair, int, double>);
+	static_assert(!tnt::is_pairish_of_v<const CustomPair&, int, double>);
+
+	static_assert(!tnt::is_pairish_of_v<TupleClass, int, float>);
+	static_assert(!tnt::is_pairish_of_v<std::tuple<int, int>, int, int>);
+	static_assert(!tnt::is_pairish_of_v<Test, int, int>);
+	static_assert(!tnt::is_pairish_of_v<int, int, int>);
+	static_assert(!tnt::is_pairish_of_v<E, int, int>);
+	static_assert(!tnt::is_pairish_of_v<const_int, int, int>);
+
 	static_assert(tnt::is_tuplish_of_pairish_v<std::tuple<>>);
 	static_assert(!tnt::is_tuplish_of_pairish_v<std::tuple<int>>);
 	static_assert(tnt::is_tuplish_of_pairish_v<std::tuple<std::pair<int, int>>>);