one_of.hpp

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#ifndef EAGINE_VALID_IF_ONE_OF_HPP
#define EAGINE_VALID_IF_ONE_OF_HPP
 
#include "decl.hpp"
 
namespace eagine {
 
// one of
template <typename T, T... C>
struct valid_if_one_of_policy {
    auto operator()(const T& value) const noexcept {
        const T choices[] = {C...};
        for(const T& choice : choices) {
            if(value == choice) {
                return true;
            }
        }
        return false;
    }
 
    struct do_log {
        template <typename X, typename = disable_if_same_t<X, do_log>>
        constexpr do_log(X&&) noexcept {}
 
        template <typename Log>
        void operator()(Log& log, const T& v) const {
            log << "Value " << v << ", "
                << "other than one of the values [";
 
            const T choices[] = {C...};
            bool first = true;
            for(const T& choice : choices) {
                log << (first ? "" : ", ") << choice;
                first = false;
            }
            log << "] is invalid";
        }
    };
};
 
template <typename T, T... C>
using valid_if_one_of = valid_if<T, valid_if_one_of_policy<T, C...>>;
 
} // namespace eagine
 
#endif // EAGINE_VALID_IF_ONE_OF_HPP