CODEWITHSUNDEEP
c++11
Sriram
Sriram

Reputation: 99

Delegating constructors without initialization

I am trying to implement delegated constructor without initialization. This is because I need the appropriate values obtained by a function call. How do I write a proper code without code repetition?

class foo
{
  private:
    // Something
  public:
    foo() = delete;
    foo(double a, double b, double c) 
    {
    // Something
    }
    foo(int n)
    {
    double a, b, c;
    // a, b, c passed by reference and appropriate value is obtained here.
    function_call(n, a, b, c); 
    // construct this object as if the call is foo(a, b, c) now
    foo(a, b, c); // ??? Does this work?
    }
};

Upvotes: 0

Views: 32

Answers (1)

R Sahu
R Sahu

Reputation: 206617

foo(a, b, c); // ??? Does this work?

No, it does not work. It creates a temporary object and fails to initialize the member variables of the current object.

My suggestion:

Change function_call to return a std::tuple<double, double, double> instead of updating the values of objects passed by reference.

Then, you can use:

class foo
{
   private:

      foo(std::tuple<double, double, double> const& t) : foo(std::get<0>(t), std::get<1>(t), std::get<2>(t)) {}

   public:

      foo() = delete;

      foo(double a, double b, double c) 
      {
         // Something
      }

      foo(int n) : foo(function_call(n)) {}

};

You may also use std::array<double, 3> as the return value of function_call and update the constructor accordingly.

foo(std::array<double, 3> const& arr) : foo(arr[0], arr[1], arr[2]) {}

Upvotes: 1

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