Object Oriented Programming

Object-Oriented Programming

What you'll learn

This guide covers classes, fields, methods, inheritance, polymorphism, and LP's compile-time checked private and protected access rules.

Prerequisites

• Read Language Basics first.

Syntax And Concepts

Declaring a class

LP classes use Python-like syntax with field declarations and methods.

class Entity:
    x: float = 0.0
    y: float = 0.0

    def move(self, dx: float, dy: float) -> float:
        self.x = self.x + dx
        self.y = self.y + dy
        return self.x

Instantiation

Create an object by calling the class name:

player = Player()

The current examples use default field values rather than custom constructor methods.

Inheritance

Subclasses can inherit from a base class:

class Player(Entity):
    health: int = 100

Polymorphism

Methods can be overridden in subclasses. The regression suite verifies inherited and overridden behavior.

Access control

LP checks member visibility at compile time.

• private: accessible only inside the declaring class.
• protected: accessible inside the declaring class and its subclasses.
• public: the default when no access modifier is present.

The current compiler enforces these rules for:

• field reads
• field writes
• method calls

Examples

Core OOP example

This is the same style used by tests/regression/02_oop_game_engine.lp.

class Entity:
    x: float = 0.0
    y: float = 0.0

    def move(self, dx: float, dy: float) -> float:
        self.x = self.x + dx
        self.y = self.y + dy
        return self.x

class Player(Entity):
    health: int = 100
    name: str = "Hero"

    def take_damage(self, amount: int) -> int:
        self.health = self.health - amount
        return self.health

Inheritance and protected

class Dog:
    protected kind: str = "dog"

class Puppy(Dog):
    def reveal_kind(self) -> str:
        return self.kind

This pattern is verified by tests/regression/test_inheritance_access.lp.

private rejection example

class SecretBox:
    private code: int = 7

box = SecretBox()
# box.code = 9

The commented line should be treated as a compile-time error in the current compiler.

Common errors and limitations

• Access control is compile-time enforced. If you try to touch a private or protected member from the wrong scope, the compiler should reject it.
• protected is designed for subclass access, not unrestricted same-file access.
• The public docs focus on field defaults and methods. More elaborate object-construction patterns are possible in source, but they are not the center of the verified example set yet.
• Exported C APIs skip private functions and top-level names that start with _ by convention.

See also

• Expressions and Collections
• [Error Handling and Advanced Control Flow]
• Examples Cookbook
• Language Reference