Attempt to create an operator||=

test.cpp

// -*- compile-command: "clang++ -Weverything -Wno-c++98-compat -ggdb -o test -std=c++11 -stdlib=libc++ test.cpp" -*-

#include <iostream>
#include <type_traits>

template <typename T, typename U, bool boolable = std::is_convertible<T,bool>::value, bool assignable = std::is_assignable<T, U>::value >
struct or_assign_helper;

template <typename T, typename U>
struct or_assign_helper<T, U, true, true> {
	static T&& compute(T&& t, const U&& u) {
		if (!t) {
			t = u;
		}

		return std::forward<T>(t);
	}
};

//replace or_assign with operator of your choice
template <typename T, typename U>
T&& or_assign(T&& t, const U&& u) {
	return or_assign_helper<T, U>::compute(std::forward<T>(t), std::forward<const U>(u));
}

struct Foo {
	operator int() const { return 42; }
	operator const char*() const { return "this shouldn't get used"; }
};

int main(const int argc, const char* argv[]) {
	int foo = argc - 1;
	or_assign(foo, Foo());
	std::cout << "Test: " << foo << std::endl;
	or_assign(argv[argc-1], Foo());
	std::cout << "String test: " << argv[argc-1] << std::endl;
	return 0;
}