240426 C++ attribute [[nodiscard]]

https://stackoverflow.com/questions/76489630/explanation-of-nodiscard-in-c17

标记有返回值的函数，提醒程序员需要用函数的返回值，隐含的意思是函数不是直接作用在对象本身

Discussion

An example of good use for [[nodiscard]] can be object methods that manipulate an object, but provide the result in a copy. Example:

DateTime yesterday = DateTime.now().substractOneDay();
std::cout << "Yesterday was " << yesterday.nameOfDay() << std::endl;

vs:

DateTime yesterday = DateTime.now();
yesterday.substractOneDay();
std::cout << "Yesterday was " << yesterday.nameOfDay() << std::endl;

A [[nodiscard]] would tell the programmer of the second example, that they are using it wrong.