具有指针类型和常规类型的类模板 [英] Class template with both pointer type and regular type
问题描述
我用值类型的模板定义一个Node类
I define a Node class with template for its value type
template<class T>
class Node {
T val;
public:
Node (T & v) : val (v) {}
...
void print() { cout << v << endl; }
}
在大多数情况下，感兴趣的节点值将是一个对象类，例如class Foo.在这种情况下，使用Node<Foo *>会更方便.但是也可能是该节点将保留原始时间，例如int.然后使用Node<int>就足够了.
Most times, the node value of interest will be an object class, say class Foo. In that case, use Node<Foo *> will be more convenient. But it could also be that the node will hold primitive time, say int. Then use Node<int> will suffice.
问题是，某些功能可能需要根据T是否为指针类型而有所不同.例如，print应当为cout << *v，否则为cout << v.
The problem is, some of the function may need to behave differently based on whether T is a pointer type or not. For example, print should cout << *v when it is and cout << v otherwise.
我试图定义两者:
template<class T>
class Node {
T val;
public:
Node (T & v) : val (v) {}
...
void print() { cout << v << endl; }
}
template<class T>
class Node<T*> {
T* val;
public:
Node (T* v) : val (v) {}
...
void print() { cout << *v << endl; }
}
现在它可以根据是否为Node<int> or Node<int *>选择适当的定义，但是问题是，这两个定义将共享许多代码.我想知道是否有更好的方法来实现这一目标.
It now can choose the appropriate definition based on whether it's Node<int> or Node<int *> But the problem become, the two definitions will share many code. I'm wondering whether there's better way to achieve this.
推荐答案
请参见:此处应使用相同的技术，在这两种情况下，您都可以将val作为参考(或指针)统一处理.
The same technique should work here, allowing you to deal with the val as a reference (or a pointer) uniformly in both cases.
CRTP 可以帮助减少代码重复，从而允许两个专业化的通用代码而没有任何开销，也是如此.
CRTP may help reduce code duplication, allowing for common code for two specializations without any overhead, as well.
请注意，当您有时使用指针而有时使用实例时，所有权语义会变得棘手-如果val有时是参数的指针，而有时又是参数的副本，那么val的寿命是多少，以及如何执行?
Note that ownership semantics get tricky when you sometimes use a pointer and sometimes an instance -- what is the lifetime of val if sometimes it is a pointer of an argument, and other times it is a copy of the argument, and how to you enforce it?
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