Abstract Structs

Abstract structs in Kiwi serve as a way to define structs that cannot be instantiated on their own but can be used as a base for other structs. These structs are intended to outline a set of methods and properties that derived structs must implement or inherit.

Defining Abstract Structs

To define an abstract struct, use the abstract struct keywords followed by the struct name. Abstract methods within these structs are declared using the abstract def keywords.

abstract struct Shape
  abstract fn area() end
  abstract fn perimeter() end
end

Implementing Abstract Structs

When you inherit from an abstract struct, you must provide implementations for all the abstract methods defined in the base struct.

Use the override keyword to override the abstract method with an implementation.

struct Circle < Shape
  fn new(radius)
    @radius = radius
  end

  override fn area()
    return 3.14159 * @radius * @radius
  end

  override fn perimeter()
    return 2 * 3.14159 * @radius
  end
end

Instantiation

Abstract structs cannot be instantiated directly. An attempt to create an instance of an abstract struct will result in an error. Instead, you must instantiate a child struct that implements all abstract methods of the base struct.

# This will result in an error:
# shape = Shape.new()

# Correct way to instantiate:
circle = Circle.new(5)
println(circle.area())       # Output: Area of the circle.
println(circle.perimeter())  # Output: Perimeter of the circle.

Notes

• Abstract structs are a foundational concept for enforcing a contract for child structs, ensuring that they implement specific methods.
• While you cannot create instances of abstract structs, they are crucial for designing a clear and consistent struct hierarchy in object-oriented programming in Kiwi.