The Modern C++ Challenge

20. Container any, all, none

The requirement to be able to check the presence or absence of a variable number of arguments suggests that we should write variadic function templates. However, these functions require a helper function, a general-purpose one that checks whether an element is found in a container or not and returns a bool to indicate success or failure. Since all these functions, which we could call contains_all, contains_any, and contains_none, do is apply logical operators on the results returned by the helper function, we would use fold expressions to simplify the code. Short circuit evaluation is enabled after the expansion of the fold expression, which means we are evaluating only the elements that lead to a definitive result. ...