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#pragma once

////////////////////////////////////////////////////////////////////////////////////////////////////

namespace hytlass::detail {

/// @brief A bool constant that depends on one or more template parameters.
///
/// For more detailed documentation and use cases,
/// please see `dependent_false` below.
template <bool Value, class... Args>
inline constexpr bool dependent_bool_value = Value;

/// @brief An always-false value that depends on one or more template parameters.
///
/// This exists because `static_assert(false);` always fails,
/// even if it occurs in the `else` branch of an `if constexpr`.
/// The following example shows how to use `dependent_false` in that case.
///
/// @code
/// template<class T>
/// void foo (T t)
/// {
///     if constexpr (std::is_integral_v<T>) {
///         do_integer_stuff(t);
///     }
///     else if constexpr (std::is_floating_point_v<T>) {
///         do_floating_point_stuff(t);
///     }
///     else {
///         static_assert(dependent_false<T>, "T must be "
///             "an integral or floating-point type.");
///     }
/// }
/// @endcode
///
/// This implements the C++ Standard Library proposal P1830R1.
///
/// https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1830r1.pdf
///
/// That proposal is under review as of 2022/12/05.
/// The following link shows P1830's current review status.
///
/// https://github.com/cplusplus/papers/issues/572
///
/// P2593R0 proposes an alternate solution to this problem,
/// that would change the C++ language itself.
///
/// https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2593r0.html
///
/// For headers in this library, however, we only consider library solutions
/// as work-arounds for future C++ features.
template <class... Args>
inline constexpr bool dependent_false = dependent_bool_value<false, Args...>;

}  // end namespace hytlass::detail
