Which is best for a repeating piece of code?

Question

I have a class with two member functions that share a piece of code:

void A::First()
{
   firstFunctionEpilogue();
   sharedPart();
}

void A::Second()
{
   secondFunctionEpilogue();
   sharedPart();
}

Currently firstFunctionEpilogue(), secondFunctionEpilogue() and sharedPart() are not function calls but just pieces of code, sharedPart() code being duplicated. I want to get rid of the duplication.

The shared piece of code doesn't need access to any members of the class. So I can implement it as any of the three:

• a static member function,
• a const non-static member function or
• a local function.

Which variant is better and why?

Answer 1

If your function accesses state but does not change it then use a const member function.

Your case:

If it your function 1) doesn't need access to any member of the code, and 2) is related to that class, then make it a static function of your class.

That way it is clear that it is not modifying state, nor based on the state of the object.

An extra case you didn't mention:

There is another thing you can do too. And that is to make your SharedPart take in a member function pointer and to call it and then process it's main body. If you have a lot of First(), Second(), Third(), Fourth(), ... such functions then this can lead to less code duplication. That way you don't need to keep calling SharedPart(); at the end of each member function, and you can re-use First(), Second(), THird(), ... without calling the SharedPart() of the code.