Will below code be compiled successfully? Explain why?

 Code: 

class MainClass {
    func mainClassFunction() {
        print("mainClassFunction")
    }
}
class SubClass: MainClass {
    func subClassFunction() {
        print("subClassFunction")
    }
}
extension SubClass {
    override func mainClassFunction() {
        print("extension")
    }
}

Answer: Will Not compile.

The provided code will not compile. 

Reason:

In Swift, extensions cannot override methods that are defined in the superclass. Overrides are a feature of subclassing and must be declared within the subclass itself, not in an extension. 

Explanation:

1. The MainClass Definition:

   - The MainClass contains a method mainClassFunction().

2. The SubClass Definition:

   - The SubClass inherits from MainClass and can override mainClassFunction() if needed (but doesn't in this code).

3. The Extension:

   swift

   extension SubClass {

       override func mainClassFunction() {

           print("extension")

       }

   }

   

   Here, the extension attempts to override the mainClassFunction() from MainClass. This results in a compiler error because Swift does not allow method overrides in extensions.

   This restriction exists because extensions are intended to add functionality, not alter or replace existing functionality of the class hierarchy.

Correct Approach:

To override mainClassFunction(), the override must be declared directly within the SubClass:

swift

class SubClass: MainClass {

    override func mainClassFunction() {

        print("extension")

    }

}

Conclusion:

The code will not compile because overriding a method in an extension is not allowed in Swift. Overrides must occur within the subclass itself.