Support indexing util::array with arbitrary array-like types

libs/util/include/psemek/util/array.hpp

@@ -9,6 +9,38 @@
 namespace psemek::util
 {
 
+	namespace detail
+	{
+
+		template <typename T, typename = void>
+		struct is_array : std::false_type {};
+
+		template <typename T>
+		struct is_array<T, std::void_t<decltype(std::declval<T&>()[0])>>
+			: std::true_type
+		{};
+
+		template <typename T>
+		constexpr bool is_array_v = is_array<T>::value;
+
+		template <typename ... Ts>
+		struct is_index;
+
+		template <>
+		struct is_index<>
+			: std::false_type
+		{};
+
+		template <typename T, typename ... Ts>
+		struct is_index<T, Ts...>
+			: std::bool_constant<!is_array_v<T>>
+		{};
+
+		template <typename ... Ts>
+		constexpr bool is_index_v = is_index<Ts...>::value;
+
+	}
+
 	template <typename T, std::size_t N>
 	struct array
 	{
@@ -62,14 +94,27 @@ namespace psemek::util
 			return dims_[2];
 		}
 
-		T & operator()(dims_type const & index);
+		template <typename Index>
-		T const & operator()(dims_type const & index) const;
+		std::enable_if_t<detail::is_array_v<Index>, T &>
+			operator()(Index const & index);
+
+		template <typename Index>
+		std::enable_if_t<detail::is_array_v<Index>, T const &>
+			operator()(Index const & index) const;
 
 		template <typename ... Ixs>
-		T & operator()(Ixs ... ixs);
+		std::enable_if_t<detail::is_index_v<Ixs...>, T &>
+			operator()(Ixs ... ixs);
 
 		template <typename ... Ixs>
-		T const & operator()(Ixs ... ixs) const;
+		std::enable_if_t<detail::is_index_v<Ixs...>, T const &>
+			operator()(Ixs ... ixs) const;
+
+		template <typename I>
+		T & operator()(std::initializer_list<I> const & index);
+
+		template <typename I>
+		T const & operator()(std::initializer_list<I> const & index) const;
 
 		array copy() const;
 
@@ -127,8 +172,8 @@ namespace psemek::util
 			return false;
 		}
 
-		template <std::size_t N>
+		template <std::size_t N, typename Index>
-		std::size_t index(std::array<std::size_t, N> const & i, std::array<std::size_t, N> const & dims)
+		std::size_t index(Index const & i, std::array<std::size_t, N> const & dims)
 		{
 			std::size_t r = 0;
 			for (std::size_t d = N; d --> 0;)
@@ -278,20 +323,25 @@ namespace psemek::util
 	}
 
 	template <typename T, std::size_t N>
-	T & array<T, N>::operator()(dims_type const & index)
+	template <typename Index>
+	std::enable_if_t<detail::is_array_v<Index>, T &>
+		array<T, N>::operator()(Index const & index)
 	{
 		return data_[detail::index(index, dims_)];
 	}
 
 	template <typename T, std::size_t N>
-	T const & array<T, N>::operator()(dims_type const & index) const
+	template <typename Index>
+	std::enable_if_t<detail::is_array_v<Index>, T const &>
+		array<T, N>::operator()(Index const & index) const
 	{
 		return data_[detail::index(index, dims_)];
 	}
 
 	template <typename T, std::size_t N>
 	template <typename ... Ixs>
-	T & array<T, N>::operator()(Ixs ... ixs)
+	std::enable_if_t<detail::is_index_v<Ixs...>, T &>
+		array<T, N>::operator()(Ixs ... ixs)
 	{
 		dims_type dims{static_cast<std::size_t>(ixs)...};
 		return (*this)(dims);
@@ -299,12 +349,27 @@ namespace psemek::util
 
 	template <typename T, std::size_t N>
 	template <typename ... Ixs>
-	T const & array<T, N>::operator()(Ixs ... ixs) const
+	std::enable_if_t<detail::is_index_v<Ixs...>, T const &>
+		array<T, N>::operator()(Ixs ... ixs) const
 	{
 		dims_type dims{static_cast<std::size_t>(ixs)...};
 		return (*this)(dims);
 	}
 
+	template <typename T, std::size_t N>
+	template <typename I>
+	T & array<T, N>::operator()(std::initializer_list<I> const & index)
+	{
+		return data_[detail::index(std::data(index), dims_)];
+	}
+
+	template <typename T, std::size_t N>
+	template <typename I>
+	T const & array<T, N>::operator()(std::initializer_list<I> const & index) const
+	{
+		return data_[detail::index(std::data(index), dims_)];
+	}
+
 	template <typename T, std::size_t N>
 	array<T, N> array<T, N>::copy() const
 	{