possible-alias.hpp

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#pragma once
 
/// @file
/// @ingroup core
/// Utility to guard against accidental template aliases.
 
#include <type_traits>
 
namespace guanaqo {
namespace detail {
 
/// Check if @p A is equal to any of @p Bs.
template <class A, class... Bs>
constexpr bool any_is_same() {
    return (std::is_same_v<A, Bs> || ...);
}
 
/// Unused unique type tag for template specializations that were rejected
/// because some types were not distinct.
template <class...>
struct dummy;
 
} // namespace detail
 
/// If @p NewAlias is not the same type as any of @p PossibleAliases, the result
/// is @p NewAlias. If @p NewAlias is not distinct from @p PossibleAliases, the
/// result is a dummy type, uniquely determined by @p NewAlias and
/// @p PossibleAliases.
/// @ingroup core
template <class NewAlias, class... PossibleAliases>
using possible_alias_t =
    std::conditional_t<detail::any_is_same<NewAlias, PossibleAliases...>(),
                       detail::dummy<NewAlias, PossibleAliases...>, NewAlias>;
 
} // namespace guanaqo