never.hpp

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#ifndef EAGINE_VALID_IF_NEVER_HPP
#define EAGINE_VALID_IF_NEVER_HPP
 
#include "decl.hpp"
 
namespace eagine {
 
struct never_valid_policy {
 
    template <typename T>
    constexpr auto operator()(const T&) const noexcept {
        return false;
    }
 
    struct do_log {
        template <typename X, typename = disable_if_same_t<X, do_log>>
        constexpr do_log(X&&) noexcept {}
 
        template <typename Log, typename T>
        void operator()(Log& log, const T&) const {
            log << "value is not valid";
        }
    };
};
 
template <typename T>
using never_valid = valid_if<T, never_valid_policy>;
 
} // namespace eagine
 
#endif // EAGINE_VALID_IF_NEVER_HPP