Classes

Classes let you define custom types with fields and methods. CColon classes support public/private visibility, inheritance, and constructors.

Defining a class

class Animal {
    var public string name = "unknown"
    var public int age = 0
    var private string id = "internal"

    public function init(string name, int age) {
        self.name = name
        self.age = age
    }

    public function speak() string {
        return self.name + " makes a sound"
    }
}

A class body contains field declarations and method declarations.

Fields

Fields are declared with var, a visibility modifier, a type, a name, and a default value:

var public string name = "unknown"
var private int secret = 0

• public fields can be read and written from outside the class.
• private fields can only be accessed inside the class (through self).

Every field must have a default value.

Methods

Methods are functions defined inside a class. Each method has a visibility modifier:

public function greet() string {
    return "Hello, " + self.name
}

private function internal() {
    // only callable from other methods in this class
}

Inside a method, use self to access the current instance's fields and methods:

public function info() string {
    return self.name + " (age " + self.age.tostring() + ")"
}

Constructors

The init method is the constructor. It runs when you create a new instance:

class Dog {
    var public string name = ""
    var public string breed = ""

    public function init(string name, string breed) {
        self.name = name
        self.breed = breed
    }
}

var Dog d = Dog("Rex", "Labrador")

init does not return a value. The newly created instance is returned automatically.

Creating instances

Call the class name like a function, passing arguments that match the init parameters:

var Animal cat = Animal("Whiskers", 3)
console.println(cat.name)        // "Whiskers"
console.println(cat.speak())     // "Whiskers makes a sound"

Inheritance

Use extends to create a subclass:

class Dog extends Animal {
    var public string breed = "mixed"

    public function init(string name, int age, string breed) {
        super.init(name, age)
        self.breed = breed
    }

    public function speak() string {
        return self.name + " barks!"
    }
}

A subclass inherits all fields and methods from its parent. It can override methods by defining them with the same name.

Calling parent methods

Use super.methodName(args) to call a method from the parent class:

public function init(string name, int age, string breed) {
    super.init(name, age)
    self.breed = breed
}

String representation

When you call .tostring() on an instance or print it, CColon generates a string showing the class name, public fields, and public method names:

var Dog d = Dog("Rex", 5, "Labrador")
console.println(d.tostring())
// <Dog name="Rex", age=5, breed="Labrador" | speak(), info()>

Full example

import console

class Shape {
    var public string name = "shape"

    public function init(string name) {
        self.name = name
    }

    public function area() float {
        return 0.0
    }
}

class Circle extends Shape {
    var public float radius = 0.0

    public function init(float radius) {
        super.init("circle")
        self.radius = radius
    }

    public function area() float {
        return 3.14159 * self.radius * self.radius
    }
}

function main() {
    var Circle c = Circle(5.0)
    console.println(c.name)                    // "circle"
    console.println(c.area().tostring())       // "78.53975"
}