根據模板參數調用不同版本的模板成員函數

Question

我需要根據模板參數的某些靜態成員調用具有相同參數的模板成員函數的不同版本。下面是我需要做的一種簡化版本：

class A { 
public: 
    //... 
    static const char fooString[]; 
}; 
const char A::fooString[] = "This is a Foo."; 

class B { 
public: 
    //... 
    static const char barString[]; 
}; 
const char B::barString[] = "This is a Bar."; 

class C { 
public: 
    //... 
    static const char fooString[]; 
}; 
const char C::fooString[] = "This is also a Foo."; 

//Many other classes which have either a fooString or a barString 

void doFoo(const char*s) { /*something*/ } 
void doBar(const char*s) { /*something else*/ } 

template&ltclass T> 
class Something { 
public: 
    //This version should be called if T has a static member called "fooString", 
    //so it should be called if T is either class A or C 
    void doSomething() { doFoo(T::fooString); } 

    //This version should be called if T has a static member called "barString", 
    //so it should be called if T is class B 
    void doSomething() { doBar(T::barString); } 
}; 


void someFunc() 
{ 
    Something&ltA> a; 
    Something&ltB> b; 
    Something&ltC> c; 

    a.doSomething(); //should call doFoo(A::fooString) 
    b.doSomething(); //should call doBar(B::barString) 
    c.doSomething(); //should call doFoo(C::fooString) 
} 

我該如何實現這一目標？

Answer 1

一個可能的解決方案：

#include <iostream> 
#include <type_traits> 

class A { 
public: 
    //... 
    static const char fooString[]; 
}; 
const char A::fooString[] = "This is a Foo."; 

class B { 
public: 
    //... 
    static const char barString[]; 
}; 
const char B::barString[] = "This is a Bar."; 

class C { 
public: 
    //... 
    static const char fooString[]; 
}; 
const char C::fooString[] = "This is also a Foo."; 

void doFoo(const char*s) { std::cout << "doFoo: " << s << "\n"; } 
void doBar(const char*s) { std::cout << "doBar: " << s << "\n"; } 

template<class T> 
class Something { 
public: 
    //This version should be called if T has a static member called "fooString", 
    //so it should be called if T is either class A or C 
    template <typename TT = T, typename std::enable_if<TT::fooString != 0, bool>::type = false> 
    void doSomething() { doFoo(T::fooString); } 

    //This version should be called if T has a static member called "barString", 
    //so it should be called if T is class B 
    template <typename TT = T, typename std::enable_if<TT::barString != 0, bool>::type = false> 
    void doSomething() { doBar(T::barString); } 
}; 


int main() 
{ 
    Something<A> a; 
    Something<B> b; 
    Something<C> c; 

    a.doSomething(); //should call doFoo(A::fooString) 
    b.doSomething(); //should call doBar(B::barString) 
    c.doSomething(); //should call doFoo(C::fooString) 
} 

輸出：

doFoo: This is a Foo. 
doBar: This is a Bar. 
doFoo: This is also a Foo.