C ++ 11期货的多态性

Question

Say I have two futures, future<int> a and future<char> b . Is there any way to put both of these (or pointers to them) into any of the standard containers ( std::{list,vector,...} ?

The problem I intend to solve with this:

Setup: I have a thread pool library that allows the user to submit tasks in the form of arbitrary functions w/ arguments as tasks. The pool executes the function w/ args in a worker thread and the result is communicated to the user by a future<func::result_type> , where func is an std::function<?> . (? Being a wildcard, b/c it words with any function.) These futures are also the only external way to wait on a task to complete. If one only wants to wait until they execute, one must call future::get() and ignore the result.

Problem: I want to provide a way to wait on all the tasks currently in the queue. To do this, I need to keep a list of all the futures so I can call get on them.

The library I'm talking about, in case you really need context (280 loc): https://github.com/Tyler-Hardin/thread_pool

Answer 1

I don't quite understand why you would need this, but you can use a standard technique - template wrappers with common base class:

class FutureHolderBase {
public:
    virtual ~FutureHolderBase() = default;
};

template<typename T>
class FutureHolder : public FutureHolderBase {
private:
    std::future<T> m_future;
};

int main() {
    // unfortunately can't use list-initialization here because it supports only copyable types
    std::vector<std::unique_ptr<FutureHolderBase>> v;
    v.push_back(std::make_unique<FutureHolder<int>>());
    v.push_back(std::make_unique<FutureHolder<float>>());
}