static_assert( std::is_same_v< std::tuple_element<0, decltype(tuple)>::type, Kind::EnumType > ); static_assert( std::is_same_v< std::tuple_element<1, decltype(tuple)>::type, Kind::EnumType > ); // WHAT ??? static_assert( std::is_same_v< ValueListAsTuple_t< Kind::MetaV...
constexpr if 的主要用途是简化模板代码（这也意味着除非你是库作者或者模板狂魔，很少会用到）。很多...
2.3.2.1 解释std::is_same 2.3.2.2 解释std::enable_if_t 2.3.2.3 解释两个模板函数的实例化 2.3.2.4 解释为什么加默认值=1 2.4 if constexpr的模拟 1. 什么是编译期if 编译期if是指条件变量在编译器就确定,在编译期执行的if条件。c++的编译期if语句在c++17中引入,为if constexpr. 假如编译期if命令if...
{usingTagType =typename T::tag;ifconstexpr (is_same<TagType, NumericTag>::value) { std::stringstream ss; ss<<a.data_; std::cout<< ss.str().length() <<std::endl; }elseif(is_same<TagType, StringTag>::value) { std::cout<< a.data_.length() <<std::endl; }else{return0; ...
template <typename T>T max(T a, T b) {if constexpr (std::is_same_v<T, std::string>) {return a.length() > b.length() ? a : b;} else {return a > b ? a : b;}} 在这个例子中,if constexpr使我们能够根据模板参数T的类型在编译时期选择不同的代码路径。如果T是std::string,我们...
如果传入实参类型为std::string,则肯定满足上述条件,但假如传入实参不为std::string,虽然它不满足std::is_same<T, std::string>::value,但由于if constexpr不支持短路规则,所以T::npos == -1依然会被编译。由于T::nops是个非法的表达式所以会编译失败。上述例子正确写法应该是: ...
In the Visual Studio debugger, when debugging a non-optimised Debug build, you can tell whether aconstexprfunction is being evaluated at compile time by putting a breakpoint inside it. If the breakpoint is hit, the function was called at run-time. If not, then the function was called at...
按照我的理解吧，引入constexpr关键字主要是为了增强C++对于编译期计算能力的支持，扩大了常量表达式的使用...
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(A function body that is=default;or=delete;contains none of the above.) (since C++14) (until C++23) constexprconstructor Aconstexprconstructorwhose function body is not=delete;must satisfy the following additional requirements: for the constructor of aclass or struct, every base class sub-objec...