#include <future>
#include <cassert>
class A
{
long data_;
public:
explicit A(long i) : data_(i) {}
long operator()(long i, long j) const {return data_ + i + j;}
};
int main()
{
{
std::packaged_task<double(int, char)> p0(A(5));
std::packaged_task<double(int, char)> p;
swap(p, p0);
assert(!p0.valid());
assert(p.valid());
std::future<double> f = p.get_future();
p(3, 'a');
assert(f.get() == 105.0);
}
{
std::packaged_task<double(int, char)> p0;
std::packaged_task<double(int, char)> p;
swap(p, p0);
assert(!p0.valid());
assert(!p.valid());
}
}