Classes

An object is created as an instance of class. The type of the object is its class name. An object can be implicitly converted into any type, and vice versa.

Class declarations

A class must be defined by a class declaration. A class expression is not supported. Classes are declared by using class keyword.

class Rectangle {
  height: float;
  width: float;

  constructor(height: float, width: float) {
    this.height = height;
    this.width = width;
  }

  getArea() {
    return this.height * this.width;
  }
}

A property may have a type annotation, but a type annotation is optional. In the code above, the types of properties height and width are float.

All class declarations, properties, and methods are public. No access modifiers such as private and readonly are (currently) not supported.

extends

A class can inherit from another class. extends keyword is used to specify a super class.

class Square extends Rectangle {
  constructor(sideLength: float) {
    super(sideLenght, sideLength);
  }
}

A constructor must first invokes the constructor of its super class. A subclass is a subtype of the type representing its super class.

new

new keyword is used to create a class instance.

let rect = new Rectangle(13, 15);

Properties and methods

Properties and methods are accessed using the dot notation.

print(rect.height);    // 13
print(rect.getArea()); // 195

Unlike TypeScript, a method is not a property holding a function object. It may not be accessed as a property. For example, since getArea is a method, the following code is not valid in BlueScript.

let m = rect.getArea;     // error

The rect objecrt does not have a property named getArea.

When a property's type is integer or float, an object may hold only a 30bit value as the property's value. If a class has a property of object type, an integer or float property of its subclass holds a 30bit value. Otherwise, it holds a 32bit value.

Constructors

A property must be explicitly initailized in a constructor. A property declaration (currently) must not have an initializer, which is an expression computing the initial value of that property.

class Rectangle {
  height: float = 10.0;    // error
  width: float = 10.0;     // error
}

This is valid in TypeScript, but it is not in BlueScript. = 10.0 must be erased.

In a constructor, a property is initialized through this. this is a special variable that is available only in method bodies and a constructor. It refers to their object. Unlike TypeScript, this is not available in a function body or at the top level.