SharedPtr.exchange

//lvalue exchange
{
	shared x = SharedPtr!(shared long).make(123);
	auto y = SharedPtr!(shared long).make(42);

	auto z = x.exchange(y);

	assert(x.load.get == 42);
	assert(y.get == 42);
	assert(z.get == 123);
}

//rvalue exchange
{
	shared x = SharedPtr!(shared long).make(123);
	auto y = SharedPtr!(shared long).make(42);

	import core.lifetime : move;
	auto z = x.exchange(move(y));

	assert(x.load.get == 42);
	assert(y == null);
	assert(z.get == 123);
}

//null exchange (same as move)
{
	shared x = SharedPtr!(shared long).make(123);

	auto z = x.exchange(null);

	assert(x.load == null);
	assert(z.get == 123);
}

//swap:
{
	shared x = SharedPtr!(shared long).make(123);
	auto y = SharedPtr!(shared long).make(42);

	//opAssign is same as store
	import core.lifetime : move;
	y = x.exchange(move(y));

	assert(x.load.get == 42);
	assert(y.get == 123);
}