Question

Whilst refactoring some legacy C++ code I found that I could potentially remove some code duplication by somehow defining a variable that could point to any class method that shared the same signature. After a little digging, I found that I could do something like the following:

class MyClass { protected:     bool CaseMethod1( int abc, const std::string& str )     {         cout << 'case 1:' << str;         return true;     }      bool CaseMethod2( int abc, const std::string& str )     {         cout << 'case 2:' << str;         return true;     }      bool CaseMethod3( int abc, const std::string& str )     {         cout << 'case 3:' << str;         return true;     }  public:     bool TestSwitch( int num )     {            bool ( MyClass::*CaseMethod )( int, const std::string& );          switch ( num )         {             case 1: CaseMethod = &MyClass::CaseMethod1;                     break;             case 2: CaseMethod = &MyClass::CaseMethod2;                     break;             case 3: CaseMethod = &MyClass::CaseMethod3;                     break;         }          ...          bool res = CaseMethod( 999, 'hello world' );          ...          reurn res;     } }; 

My question is – is this the correct way to go about this? Should I consider anything that Boost has to offer?

Edit…

Ok, my mistake – I should be calling the method like so:

bool res = ( (*this).*CaseMethod )( 999, 'Hello World' ); 

Answer 1

What you have there is a pointer-to-member-function. It will solve your problem. I am surprised that your ‘TestSwitch’ function compiles, as the calling syntax is slightly different to what you might expect. It should be:

bool res = (this->*CaseMethod)( 999, 'hello world' ); 

However, you might find a combination of boost::function and boost::bind makes things a little easier, as you can avoid the bizarre calling syntax.

boost::function<bool(int,std::string)> f=     boost::bind(&MyClass::CaseMethod1,this,_1,_2); 

Of course, this will bind it to the current this pointer: you can make the this pointer of the member function an explicit third parameter if you like:

boost::function<bool(MyClass*,int,std::string)> f=     boost::bind(&MyClass::CaseMethod1,_1,_2,_3); 

Another alternative might be to use virtual functions and derived classes, but that might require major changes to your code.