Classes, inheritance, and modules

Learning objective

• Structure Lucia programs with classes and multi-file imports.

Key syntax

class Animal {
    let name: string = "unknown";
    const kind: string = "animal";
    constructor(name: string) { this.name = name; }
}

class Dog extends Animal {
    func bark() { print(this.name); }
}

Examples

• Import syntax: import "./models/pet.lucia";.
• Import syntax also supports project-local files such as import "Palo.lucia";.
• Single inheritance with extends.
• Class fields may use default initializers.
• Class fields may be declared with const when they must not be reassigned.
• Use this for instance state.

Method and field access inside classes

• Explicit style:

func toString(): string {
    return this.obtenerNombreValor() + " " + this.obtenerNombrePalo();
}

• Implicit style (allowed):

func toString(): string {
    return obtenerNombreValor() + " " + obtenerNombrePalo();
}

Indexed assignment in methods

func mezclarMazo(): void {
    let n: int = len(this.mazo);
    for (let i = 0; i < n; i = i + 1) {
        let j: int = random(0, n - 1);
        let temp: Carta = this.mazo[i];
        this.mazo[i] = this.mazo[j];
        this.mazo[j] = temp;
    }
}

Common mistakes

• Forgetting that const class fields require an initializer.
• Reassigning a const field after declaration.
• Unknown class/function due to missing imports.
• Circular imports between files.
• Using list.length() instead of len(list).

Suggested practice

• Split a small domain model into 2-3 files using imports, inheritance, and initialized class fields.

Related

• declarations-let-const
• diagnostics