language-deep-dive7 min

Designing Classes

A class is a template for objects that share the same structure and behavior. In Clean Language, you declare properties at the top of the class, write a constructor that sets them, and add methods that operate on them. The compiler enforces everything.

A class with properties, a constructor, and multiple methods:

class Rectangle\n    number width\n    number height\n\n    constructor(number w, number h)\n        width = w\n        height = h\n\n    number area()\n        return width * height\n\n    number perimeter()\n        return 2.0 * (width + height)\n\n    string describe()\n        return "Rectangle " + width.toString() + "x" + height.toString() + ", area: " + area().toString()\n\nstart:\n    Rectangle r = Rectangle(5.0, 3.0)\n    print(r.describe())\n    print("Perimeter: " + r.perimeter().toString())

Rectangle 5.0x3.0, area: 15.0\nPerimeter: 16.0

Properties (width, height) are declared at the top of the class. The constructor assigns them. Methods access properties by name — no self. or this. needed. Methods can call other methods directly: describe() calls area() to avoid duplicating logic.

Each instance is independent — they share the template but have their own data:

start:\n    Rectangle small = Rectangle(2.0, 3.0)\n    Rectangle large = Rectangle(10.0, 8.0)\n\n    print("Small: " + small.describe())\n    print("Large: " + large.describe())\n\n    boolean fits = small.area() < large.area()\n    print("Small fits inside large: " + fits.toString())\n\n    number total = small.area() + large.area()\n    print("Combined area: " + total.toString())

Small: Rectangle 2.0x3.0, area: 6.0\nLarge: Rectangle 10.0x8.0, area: 80.0\nSmall fits inside large: true\nCombined area: 86.0

small and large are independent instances. Calling .area() on small uses 2.0x3.0; on large it uses 10.0x8.0. You can use instance method results in expressions, comparisons, and other calculations just like any other value.

Quick recap

Properties are declared at the top of the class body with type and name
constructor() assigns initial values — called when you create an instance
Methods access properties by name directly — no self or this keyword
Each instance is independent — its properties are separate from every other instance