refactor: move std patch into correct position

src/yycc/patch/contains.hpp

@@ -0,0 +1,45 @@
+#pragma once
+#include "../macro/feature_probe.hpp"
+
+namespace yycc::patch::contains {
+
+    /**
+     * @brief Checks if there is an element with key equivalent to key in the container.
+     * @details
+     * The polyfill to \c contains() function of unordered and ordered associative container.
+     * Because this function only present after C++ 20.
+     * This function will use our custom polyfill if the version of C++ standard you are using lower than C++ 20.
+     * Otherwise it will fallback to vanilla standard library function.
+     * @tparam TContainer
+     * The type of container. This container must have \c find() and \c end() member functions.
+     * @tparam TKey
+     * The type of key of container.
+     * If the container is a set, this type is the type of item in set.
+     * If the container is a map, this type is the key type of map.
+     * @param[in] container The reference to container to find.
+     * @param[in] key Key value of the element to search for
+     * @return True if there is such an element, otherwise false.
+     * @remarks
+     * This template function do not have constraint check.
+     * If container type has \c find() and \c end() member functions, this template function will be created without any error.
+     * However, this function should be used for standard library associative container according to its original purpose.
+     * It means that the type of container usually and should be one of following types:
+     * \li \c std::set
+     * \li \c std::multiset
+     * \li \c std::map
+     * \li \c std::multimap
+     * \li \c std::unordered_set
+     * \li \c std::unordered_multiset
+     * \li \c std::unordered_map
+     * \li \c std::unordered_multimap
+    */
+    template<class TContainer, class TKey>
+    bool contains(const TContainer& container, const TKey& key) {
+#if defined(YYCC_CPPFEAT_CONTAINS)
+        return container.contains(key);
+#else
+        return container.find(key) != container.end();
+#endif
+    }
+
+} // namespace yycc::patch::container