Bird in a bird

How many times is the destructor called?

struct bird {
    ~bird() { std::puts("in a bird"); }
};

bird in = bird(bird(bird(bird(bird()))));

Once!

Thanks to C++’s return value optimisation. You can disable this behaviour by passing -fno-elide-constructors to the compiler. Unless you’re using a standard later than C++14 then it happens regardless.

So does this mean we can’t let copy constructors cause side-effects, lest the compiler doesn’t bother calling them?

See copy elision and run the example.