Why is Explicit Method Invocation Required for Overloaded Methods in Derived Classes?

C Overload Resolution: Explicit Method Selection Required

In C , overload resolution occurs based on the argument types and the scopes in which a method is declared. To ensure accurate method selection, certain scenarios require explicit method invocation.

Consider the following example:

<code class="cpp">class A {
  public:
    int DoSomething() { return 0; }
};

class B : public A {
  public:
    int DoSomething(int x) { return 1; }
};

int main() {
  B* b = new B();
  b->A::DoSomething(); // Why this?
  // b->DoSomething(); // Why not this? (Compiler error)
  delete b;
  return 0;
}</code>

Why is the statement b->A::DoSomething(); necessary?

Understanding Overload Resolution:

In this case, the compiler considers the scope of the method when performing overload resolution. By default, it only searches within the current class's scope for a method match. In class B, the compiler finds DoSomething(int) within the current scope, which accepts a single int argument.

Explicit Invocation Required:

However, the parent class A also declares a version of DoSomething() that takes no arguments. To access this method in the derived class B, it must be explicitly invoked using the class scope operator (A::).

The statement b->DoSomething(); would fail to compile because the compiler cannot find a method named DoSomething() without arguments within the scope of class B. It incorrectly assumes that DoSomething(int) is the intended method.

Solutions:

To address this issue, one solution is to introduce the using declaration in class B. This pulls the DoSomething() method from the parent class into the derived class's scope:

<code class="cpp">class B : public A {
public:
    using A::DoSomething;
    // …
};</code>

With this modification, overload resolution can now correctly identify the desired DoSomething() method, eliminating the need for explicit invocation using b->A::DoSomething();.

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