Constexpr if statements C++17 C++17 introduces the constexpr if statement, which requires the conditional to be a constant expression. The conditional of a constexpr-if-statement will be evaluated at compile-time. If the constexpr conditional evaluates to true, the entire if-else will be replac...
ES.70: Prefer aswitch-statement to an if-statement when there is a choice ES.70:进行选择时,switch语句比if语句好...效率:switch语句执行的时常数比较运算,相比一系列if-then-else语句,通常可以更好地被优化。...Aswitchenables some heuristic consistency checking...If not, is there a defaultswitch...
其实问题就是为啥funcB明明没有定义，编译器却不会给任何报错。原因就一个词——实参依赖查找（ADL）。
Class1类里面没有是义funcA函数，当然会报错。至于funcB没报错，可能是因为你在哪里定义了这个函数。
允许expression statement(仅由表达式构成的语句) 允许静态变量的地址或引用作为常量表达式 constexpr mutex& get_mutex(bool which){ static mutex m1, m2; if (which) return m1; else return m2; } constexpr mutex& m = get_mutex(true); // OK ...
The ordinaryifstatement: Has its condition evaluated every time control reaches it, if ever Determines which of the two substatements to execute, skipping the other Requires both substatements to be well-formed regardless of which one is actually selected at runtime ...
你可以根据constexpr是否存在来强制执行不同的行为：使用SFINAE（例如，参见C++ check if statement can ...
if (a>=0) return a; else return −a; // error : if-statement in constexpr function } constexpr int bad3(int a) { sum = 0; // error : local var iable in constexpr function for (int i=0; i
2.4 if constexpr的模拟 一个和 if constexpr相近的模拟如下 struct identity { template <typename T> T operator()(T&& x) const { return std::forward<T>(x); } }; template <bool Cond> struct statement { template <typename F> void then(const F& f) { f(identity()); } temp...
If the if statement is of the form if constexpr, the value of the condition shall be a contextually converted constant expression of type bool; this form is called a constexpr if statement. If the value of the converted condition is false, the first substatement is a discarded statement...