An implementation of a dictionary type in C++ as an alias of std::unordered_map which uses a custom hash functor. This hash uses a trait type to tag specific combinations of types as transparent so that map lookups can happen using heterogenous types (like std::string and std::string_view, for instance).

dictionary.cpp

#include <string>
#include <string_view>
#include <unordered_map>

template<typename T, typename = void>
struct KeyTraits {};

template<>
struct KeyTraits<std::string, std::string_view>
{
	using IsTransparent = void;
};

template<typename O, typename T>
concept TransparentTo = requires
{
	typename KeyTraits<T, O>::IsTransparent;
};

template<typename T>
struct KeyHash : public std::hash<T>
{
	using is_transparent = void;

	template<TransparentTo<T> O>
	static constexpr size_t operator()(const O& other)
	{ return std::hash<O>{}(other); }
};

template<typename K, typename T, typename A = std::allocator<std::pair<const K, T>>>
using Dictionary = std::unordered_map<K, T, KeyHash<K>, std::equal_to<void>>;