CODEWITHSUNDEEP
c++oopraii
ComputrScientist
ComputrScientist

Reputation: 152

RAII Multiple Constructor

I just learned about RAII. From what I understand, the definition of RAII is in its name itself.For instance, (Let A be a class), consider the following function below:

void foo(){
   A a;
   a.init();
   // Do stuff with a.
   a.destroy();
}

Applaying RAII to the function above, we get:

void foo(){
  // Initializing the resource completely in a consttructor.
  A a;
  // Do stuff with a.
  // When out of scope, the destructor should be called.
}

So RAII is a good software development workflow since it reduces developer error since it takes advantage of constructor/destructor calls for resource initialization and deallocation.

Problem:

Suppose I have a class with multiple constructor, and contains data members that doesn't have a no-arg constructor to force RAII implementation. Consider the class below:

class A{
public:
  A(int arg1){
    int(arg1, GLOBAL_CONSTANT);
  }

  A(int arg1, arg2){
    init(arg1, arg2);
  }

  void init(int arg1, int arg2){
    _member = B(arg1, arg2);
  }

private:
  B _member;  // No-arg constructor member.
};

Since B also implements the RAII methodology, it doesn't have a no-arg constructor to force the user to not use an init() method later, thus _member must be initialized in a constructor list instead of init, making the the class above erroneous.

Question:

How do you exactly deal with this? What is the industry standard on dealing with this problem, if any at all?

I see the importance of RAII and don't want to compromise. Right now, the most clean solution in my head is have a single-constructor and use a factory method to generate variations. But I don't wanna rush and first takes into account experience of others, else I'll just create a nasty code.

Upvotes: 0

Views: 174

Answers (1)

b4hand
b4hand

Reputation: 9770

You must use an initializer list:

A(int arg1, arg2) : _member(arg1, arg2) {}

In C++11, you can also have constructors call each other using delegating constructors.

By the way, you should avoid using leading underscores on variable names as they are reserved if followed by a capital letter.

Upvotes: 3

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