c++ - 为什么此代码在模板特化方面有错误

Question

我想使用一个函数将参数传递给不同的类，所以我使用了类模板特化和可变函数模板，下面是代码:

#include <iostream>
using namespace std;

template <typename T0, typename T1>
class Package
{
    T0 Data0;
    T1 Data1;
public:
    Package(T0 data0, T1 data1): Data0(data0), Data1(data1) {}
    void Display()
    {
        cout << Data0 << " " << Data1 << endl;
    }
};

template <typename T0>
class Package<T0, void>
{
    T0 Data0;
public:
    Package(T0 data0): Data0(data0) {}
    void Display()
    {
        cout << Data0 << endl;
    }
};

template <>
class Package<void, void>
{
public:
    Package() {}
    void Display()
    {
        cout << "have no member" << endl;
    }
};

template <typename... Args>
void Post(Args... args)
{
    Package<Args...> pak = Package<Args...>(args...);
    pak.Display();
}

int main()
{
    int x = 5;
    float y = 0.9;
    Post(x, y);
    Post(x);
    Post();
    return 0;
}

我有这个错误:

 In instantiation of 'void Post(Args ...) [with Args = {int}]': 
 52:15: required from here 
 43:26: error: wrong number of template arguments (1, should be 2) 
 5:11: error: provided for 'template<class T0, class T1> class Package' 
 43:26: error: wrong number of template arguments (1, should be 2) 
 5:11: error: provided for 'template<class T0, class T1> class Package' 
 In instantiation of 'void Post(Args ...) [with Args = {}]': 
 53:14: required from here 
 43:26: error: wrong number of template arguments (0, should be 2) 
 5:11: error: provided for 'template<class T0, class T1> class Package' 
 43:26: error: wrong number of template arguments (0, should be 2) 
 5:11: error: provided for 'template<class T0, class T1> class Package'

package可以带2/1/0个参数，post可以提供2/1/0个参数，但是为什么会出现这个错误？谢谢。

Answer 1

尝试将默认模板参数添加到 Package

template <typename T0 = void, typename T1 = void>
class Package