SFINAE简单实例
程序员文章站
2022-03-15 12:15:59
SFINAE(Substitution failure is not an error),是C++11以来推出的一个重要概念,这里,只是简单举一个例子,可能会有人需要。 ......
SFINAE(Substitution failure is not an error),是C++11以来推出的一个重要概念,这里,只是简单举一个例子,可能会有人需要。
// 添加 scalar numeric conversion function,实现源自 C++ programming language(4th) // 用来防止使用static转换的时候,值发生改变 // there is no implicit conversion from Source to Target template <typename Target, typename Source, typename = std::enable_if_t<!std::is_reference_v<Target> && !std::is_same_v<std::common_type_t<std::decay_t<Target>, std::decay_t<Source>>, std::decay_t<Target>>, int>> inline Target narrow_cast(Source v) { static_assert(std::is_arithmetic<Source>::value, "The parameter of narrow_cast should be arithmetic"); static_assert(std::is_arithmetic<Target>::value, "The return value of narrow_cast should be arithmetic"); // using Target_U = std::remove_reference_t<Target>; // using Source_U = std::remove_reference_t<Source>; auto r = static_cast<Target>(v); if (static_cast<Source>(r) != v) throw std::runtime_error("narrow_cast<>() failed"); return r; } // there is implicit conversion from Source to Target template <typename Target, typename Source, typename = std::enable_if_t<!std::is_reference_v<Target> && std::is_same_v<std::common_type_t<std::decay_t<Target>, std::decay_t<Source>>, std::decay_t<Target>>, int>> inline constexpr std::remove_reference_t<Source> narrow_cast(Source v) { static_assert(std::is_arithmetic<Source>::value, "The parameter of narrow_cast should be arithmetic"); static_assert(std::is_arithmetic<Target>::value, "The return value of narrow_cast should be arithmetic"); return std::remove_reference_t<Source>(v); }
上一篇: 沃尔玛在美正式移动支付 支持苹果和安卓
下一篇: 苹果手表出货量真的是竞争对手之和吗