Question

当我需要定义许多类似的方法时，我的目的是避免使用宏样式。所以我很感兴趣，我可以使用模板或类似的东西吗？

这是伪c ++中的一般概念：

template <class T, class U> void myMethod(T t, U u){ ..do a lot .. }

class A {
public:
  A(){}
  void myMethod<int, int>;
  void myMethod<float, char>;

  // ... etc
};

Answer 1

template <class T, class U> class A 
{
public:
    void MemberSet( T t, U u );
};

增加：

#include <typeinfo>
#include <iostream>

using namespace std;
class A 
{
public:
    template <class T, class U> void MemberSet( T t, U u ) {
        cout << typeid(t).name() << " " << typeid(u).name() << endl;
    };
};

int main() 
{
    A a;
    a.MemberSet(5,5);
    a.MemberSet<char, long>(5,5);
}

您可能希望显式实例化

template void A::MemberSet<int, long> (int, long);

Answer 2

不，但您可以使用继承。

template <class derived_T, class T, class U>
struct base {
  void myMethod_(T t, U u) { 
    // use this to access derived class members:
    static_cast<derived_T*>(this)->
  }
};

struct a : base<a, int, int>, base<a, float, float> {
  template <class T, class U>
  void myMethod(T&& t, U&& u) {
    base<a,T,U>::myMethod_(std::forward<T>(t), std::forward<U>(u));
  }
};

Answer 3

不，但你可以：

template <class T, class U> void struct myMethodWrapper
{
    void myMethod(T t, U u){ ..do a lot .. }
};

然后：

class A : public myMethodWrapper<int, int>, 
          public myMethodWrapper<float, float>
{
};

表现相似。

Answer 4

另一种选择是将模板代码放在类之外，并从类方法中调用它。

#include <iostream>

using namespace std;

namespace myTemplates
{
  // template method 'mult(a,b)'
  // returns a*b
  template <class T1, class T2>
    T1 mult(T1 a, T2 b)
    {
      T1 result = a * b;
      return result;
    }

  // template specialization 'mult(string aString, int m)'
  // returns a string repeated m times
  template <>
    string mult<string, int>(string input, int m)
    {
      string result;
      for (int i = 0; i < m; i++)
      {
        result += input;
      }
      return result;
    }
}

class A {
  public:
    A(){}
    int    mult(int    a , int   b ) { return myTemplates::mult(a, b ) ; }
    float  mult(float  a , float b ) { return myTemplates::mult(a, b ) ; }
    string mult(string a , int   b ) { return myTemplates::mult(a, b ) ; }
};

int main(void)
{
  int    iA = 2;
  int    iB = 3;
  int    iC = 0;   // result
  float  fA = 20.1;
  float  fB = 30.3;
  float  fC = 0.0; // result
  string sA = " -blah- ";
  string sC;       // result


  iC = myTemplates::mult(iA,iB);
  cout << "mult(" << iA << ", " << iB << ") = " << iC << endl;

  fC = myTemplates::mult(fA,fB);
  cout << "mult(" << fA << ", " << fB << ") = " << fC << endl;

  sC = myTemplates::mult(sA,iB); 
  cout << "mult(" << sA << ", " << iB << ") = " << sC << endl;

  A a; 

  iC = a.mult(iA,iB);
  cout << "a.mult(" << iA << ", " << iB << ") = " << iC << endl;

  fC = a.mult(fA,fB);
  cout << "a.mult(" << fA << ", " << fB << ") = " << fC << endl;

  sC = a.mult(sA,iB);
  cout << "a.mult(" << sA << ", " << iB << ") = " << sC << endl;

  return 1;
}

输出：

  mult(2, 3) = 6
  mult(20.1, 30.3) = 609.03
  mult( -blah- , 3) =  -blah-  -blah-  -blah-
  a.mult(2, 3) = 6
  a.mult(20.1, 30.3) = 609.03
  a.mult( -blah- , 3) =  -blah-  -blah-  -blah-

是否可以在c ++中通过模板声明方法？

4 个答案: