[英]Pass class Constructor through template argument in C++
I know function can pass through template
argument, can I pass class Constructor like this. 我知道函数可以通过
template
参数,我可以像这样传递类Constructor。
Update: The whole reason that I want to do this, is I can choose constructor in memory pool and without any code changing in the class I want to alloc (in this case class A
) 更新:我想要这样做的全部原因是,我可以在内存池中选择构造函数,而在我想要分配的类中没有任何代码更改(在本例中为
class A
)
class A
{
public:
A(){n=0;}
explicit A(int i){n=i;}
private:
int n;
};
class MemoryPool
{
public:
void* normalMalloc(size_t size);
template<class T,class Constructor>
T* classMalloc();
};
template<class T,class Constructor>
T* MemoryPool::classMalloc()
{
T* p = (T*)normalMalloc(sizeof(T));
new (p) Constructor; // choose constructor
return p;
}
MemoryPool pool;
pool.classMalloc<A,A()>(); //get default class
pool.classMalloc<A,A(1)>();
You cannot pass around constructors, but you can pass around factory functors: 你不能传递构造函数,但你可以传递工厂仿函数:
class A
{
int n;
A(int i) : n(i) {};
public:
static A* makeA(int i)
{
return new A(i);
}
};
template<typename T, typename Factory>
T* new_func(Factory factory)
{
return factory();
}
#include <functional>
int main()
{
new_func<A>(std::bind(&A::makeA, 0));
new_func<A>(std::bind(&A::makeA, 1));
}
Your whole assumption is wrong. 你的整个假设是错误的。 You don't need that feature.
您不需要该功能。
template<class T>
T* new_func()
{
return new T;
}
The thing after new
is a type, not a constructor reference. new
之后的东西是一个类型,而不是构造函数引用。
This way better I think 这种方式我觉得更好
template<class T, int n>
struct Factory
{
static T* new_func()
{
return new T(n);
}
};
template<class T>
struct Factory<T,0>
{
static T* new_func()
{
return new T;
}
};
T* t = Factory<T>::new_func(); //call default constructor
T* t2 = Factory<T,2>::new_func(); //call constructor T(2)
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