Home/

...

/

Constructor Delegation

Constructor Delegation

Learn how one constructor of a class can invoke another constructor of the same class

What it is

Constructor delegation is when one constructor of a class invokes another constructor of the same class. There, that’s simple enough!

How it is implemented

Let’s look at an example of how one constructor of a class may invoke another constructor of the same class.

C++
#include <iostream>
using namespace std;
class Collector {
  private:
    int size;
    int capacity;
    int* list;
  public:
    Collector() : Collector(0) {}
    Collector(int cap) : capacity(cap), size(0)  {
      if (cap > 0) {
        list = new int[cap];
      }
      else
        capacity = 0;
    }
    bool append(int v) {
      if (size < capacity) {
        list [ size++ ] = v;
        return true;
      }
      else
        return false;
    }
    ~Collector() {
      if (capacity > 0) {
        delete[] list;
      }
    }
};
int main() {
  // A useless Collector object of 0 capacity
  Collector c1;
  // Another Collector object, this time with a capacity of 10
  Collector c2(10);
  for(int i = 0 ; i < 15 ; i++) {
    cout << c2.append(i) << endl;
  }
  return 0;
}

We have defined a parameterized constructor on lines ...