SwaziLang OOP: Inheritance (rithi)

Inheritance is a key concept in Object-Oriented Programming (OOP).
It lets you create a new class (child/derived) that inherits properties and methods from another class (parent/base), so you can reuse and extend code efficiently.

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Analogy: Inheritance as Family Traits

Imagine a family:

• The parent has certain traits (hair color, eye color, skills).
• The child inherits those traits, but can also have their own unique features.

In SwaziLang, inheritance lets you build new classes from existing ones, gaining all their features automatically.

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What is Inheritance (rithi) in SwaziLang?

• Base class: The original blueprint (parent).
• Derived class: The new blueprint (child) that extends the base.
• Derived classes get all the properties and methods of the base class, and can add or override their own.

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Syntax

Direct Inheritance (Parentheses)

muundo Base {
    // base properties and methods
}

muundo Derived(Base) {
    // derived properties and methods
}

Using the rithi Keyword

muundo Derived rithi Base {
    // derived properties and methods
}

Both patterns work and mean the same thing.

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Constructor Chaining: supa

When a derived class has a constructor, you often want to call the parent class's constructor to set up inherited features.
Use the supa keyword for this.

muundo University {
    University(uni_name) {
        $.uni_name = uni_name
    }
}

muundo Dipartment(University) {
    Dipartment(uni_name, department_name) {
        supa(uni_name)      // calls University constructor
        $.department_name = department_name
    }
}

• supa(...) always calls the immediate base class constructor.

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Why Use Inheritance?

• Code Reuse: Avoid duplication; share common logic.
• Extension: Add or override new features for specific cases.
• Organization: Model real-world relationships.

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Practical Example

muundo Animal:
    name
    Animal(name):
        $.name = name
    tabia speak {
        chapisha `${$.name} makes a sound`
    }

muundo Dog(Animal):
    breed
    Dog(name, breed):
        supa(name)
        $.breed = breed
    tabia speak {
        chapisha `${$.name} barks!`
    }

data pet = unda Dog("Bingo", "Maltese")
pet.speak()      // Bingo barks!

• Dog inherits from Animal.
• Dog overrides the speak method.

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Tips and Warnings

• You can only inherit from one base class (no multiple inheritance).
• Use supa(...) inside the child constructor to initialize the parent.
• The derived class gets all public, locked, and static members from the base class, but not private members (@).
• You can override methods by defining them again in the derived class.

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Practice Challenge

Define a Vehicle class and a Car class that inherits from it.
Vehicle has a method move, and Car overrides it.

Solution

muundo Vehicle:
    Vehicle():
        // constructor
    tabia move {
        chapisha "Vehicle is moving"
    }

muundo Car(Vehicle):
    Car():
        supa()
    tabia move {
        chapisha "Car is driving"
    }

data v = unda Vehicle()
data c = unda Car()
v.move()     // Vehicle is moving
c.move()     // Car is driving

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Summary:

• Use inheritance to build on existing classes.
• Choose either muundo Derived(Base) or muundo Derived rithi Base.
• Use supa(...) in the child constructor to initialize the base class.
• Override methods to customize behavior.