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Tip of the Day
Language: .NET
Expertise: Beginner
Mar 2, 2004

Avoid Code Repetition by Using Pointers to Members

Suppose a class requires a "springboard" for calling a set of member functions which share the same signature. For example, the springboard might create some parameters to pass to these member functions, and might catch and process exceptions thrown by these members.

Rather than write this springboard into each member, it's preferable to implement it as a function object whose constructor has passed a pointer to the object whose member function will be invoked, the address of the method, and whose call operator [operator()] actually does the springboard work and invokes the member.

For example, suppose you've got a class X with lots of methods having the same signature as int X::one() and suppose the springboard class is UseX. You'd use the springboard like this:


   X x;
   UseX xOne(&x, &X::one);
   xOne();  // invoke X::one via the springboard

class UseX requires private data members:
   X* pX;  // the object whose member we will call
   int (X::*pF)();   // the pointer-to-member
and the call operator would look like this:
  // springboard work pre call . . .
  (pX->*pF)();  // ugly syntax! note the brackets too
  // springboard work post call . . .
This is a great way to centralise your springboard work.
St. John Kettle
 
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