c++ - 是否可以根据构造函数中作为参数传入的 bool 将数据成员初始化为 const？

Question

我有一个类，它接受一个名为 fixed 的 bool 值作为参数。如果 fixed 为 true，我希望它将数据成员 position 初始化为 const。这可能吗？

class PhysicsVertex 
{
public:
    PhysicsVertex(olc::vf2d position, const bool fixed = false) :
          position(position), fixed(fixed)
    {
    }
    olc::vf2d position; //make this const if fixed is true.
    const bool fixed = false;
};

int main()
{
    PhysicsVertex v1{ {0, 0}, true }; //initialize v1.position as const
    PhysicsVertex v1{ {0, 0} }; //initialize v1.position as non-const
}

Answer 1

如果在编译时需要有关fixed参数的信息，那么您可以使用模板

#include <type_traits>

struct vf2d
{
};
template <bool fixed>
class PhysicsVertex
{
public:
    PhysicsVertex() :
        position()
    {
    }
    typename std::conditional<fixed, const vf2d, vf2d>::type position;
};

void foo()
{
    auto vertex = PhysicsVertex<true>();
    //  vertex.position = vf2d(); - compile time error, you cannot change const member
    auto vertex2 = PhysicsVertex<false>();
    vertex2.position = vf2d(); // It works fine, you can change non const member
}