文章目录

• 目的
• 实现
• 测试

目的

类型特征的主要作用就是在编译时根据类型来做决定. 这使得代码更加清晰, 可维护.

实现

class NullType {};

template<typename T>
class TypeTraits
{
private:
    template<class U> struct PointerTraits
    {
        enum { result = false };
        typedef NullType PointeeType;
    };

    template<class U> struct PointerTraits<U*>
    {
        enum { result = true };
        typedef U PointeeType;
    };

    template<class U> struct ReferenceTraits
    {
        enum { result = false };
        typedef NullType ReferencedType;
    };

    template<class U> struct ReferenceTraits<U&>
    {
        enum { result = true };
        typedef U ReferencedType;
    };

public:
    enum { isPointer = PointerTraits<T>::result
         , isReference = ReferenceTraits<T>::result };
    typedef typename PointerTraits<T>::PointeeType PointeeType;
    typedef typename ReferenceTraits<T>::ReferencedType ReferencedType;
};

测试

#include <iostream>
#include <vector>

using namespace std;

int main(int argc, char* argv[])
{
    const bool isPointer = TypeTraits<vector<int>::iterator>::isPointer;
    cout << (isPointer ? "pointer" : "not pointer") << endl;

    const bool isRef = TypeTraits<int&>::isReference;
    cout << (isRef ? "ref" : "not refer") << endl;

    return 0;
}

输出

not pointer
ref