初始化std :: variant ？

Question

我有一堂课，看起来像这样：

class X
{
  std::variant<CComPtr<ID2D1HwndRenderTarget>, CComPtr<ID2D1DCRenderTarget>> mpRenderTarget;
  void init();
}

// To early to know which member we need, it's no value until derived class calls init() method.
X::X() : mpRenderTarget(nullptr)

void X::init()
{
   // Only here it is known what exactly to initialize!
   // and this is going to be in derived class, this one pure virtual.
}

问题是此构造函数无法编译，因为变量初始化无效，但是，如果我省略了构造函数中mpRenderTarget的初始化，那么另一个问题是根据标准，变体为“未变形”。

我只想将其初始化为构造函数中的某些默认值，但是如何？

Answer 1

简单地为它分配类型的默认值one