when_all does not support continuing futures that return void #79
Description
The following code fails to compile on VS2015 Update 3. If futures are changed to take and return ints, then everything works.
#include <stlab/concurrency/concurrency.hpp>
#include <iostream>
int main(int argc, char *argv[])
{
std::cout << "1\n";
auto future = stlab::async(stlab::default_executor, [] {std::cout << "2\n"; });
auto future2 = future.then([] {std::cout << "3\n"; }).then([] {std::cout << "5\n"; });
auto future3 = future.then([] {std::cout << "4\n"; });
auto future4 = stlab::when_all(stlab::default_executor, [] {std::cout << "6\n"; }, future2, future3);
std::cout << "7\n";
while (!future4.get_try());
return 0;
}