Most elegant way to write a one-shot 'if'

Question

Since C++ 17 one can write an if block that will get executed exactly once like this:

#include 

        

Answer 1

Like @damon said, you can avoid using std::exchange by using a decrementing integer, but you have to remember that negative values resolve to true. The way to use this would be:

if (static int n_times = 3; n_times && n_times--)
{
    std::cout << "Hello world x3" << std::endl;
} 

Translating this to @Acorn's fancy wrapper would look like this:

struct n_times {
    int n;
    n_times(int number) {
        n = number;
    };
    explicit operator bool() {
        return n && n--;
    };
};

...

if(static n_times _(2); _)
{
    std::cout << "Hello world twice" << std::endl;
}