具有可变函数参数的 C++ 多态性

我正在与您分享一个使用可变参数函数参数的类遇到的问题。它是下面代码中所示的 Thread 类。它是 std::thread 的包装器，以便使用函数模式。

我想在这个函数中使用多态性，将 Thread 类继承到一个新类 Functor 中，但是 gcc 返回以下错误：

#include <thread>
#include <iostream>

using namespace std;

template<class... Args>
class Thread
{
public:
    virtual void operator()(Args...) = 0;

    void run(Args... args)
    {
    std::thread t(std::forward< Thread<Args...> >(*this), std::forward<Args>(args)...);
    t.join();
    }
};

template<class... Args>
class Functor : public Thread<Args...>
{
public:
    // generates the errors bellow
    virtual void operator()(Args... /*args*/)
    {
    }

    // doesnot work since the pure virtual function wants another prototype of function.
    // void operator()(int)
    // {
    // }
};

int main()
{
    int a = 12;
    Functor<int> f;
    f.run(ref(a));

    return 0;
}

from t-Thread-args2.cpp:1:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/tuple: In instantiation of ‘struct std::_Head_base, false>’:
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/tuple:215:12:   required from ‘struct std::_Tuple_impl, int>’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/tuple:507:11:   required from ‘class std::tuple, int>’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/functional:1601:39:   required from ‘struct std::_Bind_simple(int)>’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/thread:133:9:   required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = Thread; _Args = {int}]’
t-Thread-args2.cpp:14:83:   required from ‘void Thread::run(Args ...) [with Args = {int}]’
t-Thread-args2.cpp:42:17:   required from here
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.7.2/../../../../include/c++/4.7.2/tuple:166:13: error: cannot declare field ‘std::_Head_base, false>::_M_head_impl’ to be of abstract type ‘Thread’
t-Thread-args2.cpp:7:7: note:   because the following virtual functions are pure within ‘Thread’:
t-Thread-args2.cpp:10:18: note:     void Thread::operator()(Args ...) [with Args = {int}]
  

我真的不明白这个错误，因为纯虚函数在派生类中定义良好。但是，将函数 run() 移至派生类 (Functor) 时它可以工作。

提前致谢， 坎纳

根据 [thread.thread.constr]§3，第一个参数的类型std::thread构造函数是F&&，要求F is MoveConstructible。就你而言，F is Thread，这不是MoveConstructible.

换句话说，std::thread需要按值存储函子，并且您将函子转发为Thread，这是抽象的。