c++ parameter pack specification in constructor rather than template

Question

Unlike function declarations with parameter packs, I've found that classes require the type for each argument in the angle brackets...

Component<IntegerPair, int, int> temp(40, 5);

...which seems redundant. Here's how I defined Component:

template<typename T, class... T_Args>
class Component
{
public:
  Component(T_Args... args)
    : m_data(args...)
  {}

  T m_data;
};

1. Is there a way to remove int, int from the above statement?
2. If so, is it ok to remove it?
3. Also, is my way of instantiation m_data safe? When using std::forward<T_Args>(args)... my compiler told me I didn't have a constructor that could convert all of the argument types.

Answer 1

One way is to make the constructor a template:

#include <utility>

struct IntegerPair {
    IntegerPair(int, int) {}
};

template<typename T>
class Component
{
public:
  template<typename... T_Args>
  Component(T_Args&&... args)
    : m_data(std::forward<T_Args>(args)...)
  {}

  T m_data;
};

int main()
{
    Component<IntegerPair> c {1,2};
}

This is functionally equivalent to std::vector and its member function emplace_back. It's perfectly ok, IMO. The error messages are pretty cryptic, as usual in template constructs like this, but this can be mitigated with an appropriate static_assert.