Sample code for https://github.com/fish-shell/fish-shell/issues/1529#issuecomment-50243611

gistfile1.cpp

#include <iostream>

class Foo {
    public:
        Foo() { std::cout << "Foo::Foo()" << std::endl; }
        Foo(const Foo& y) { std::cout << "Foo::Foo(const Foo&)" << std::endl; }
};

void func(const Foo& ref) { }

int main() 
{
    Foo *tmp = new Foo();
    bool flag = true;
    func(flag ? *tmp : Foo()); // This will invoke copy constructor
    //func(*tmp);   // This will not invoke copy constructor
}