Classes.md

Classes

Like other Object-Oriented programming languages, Dove support classes. A class is a reusable template for creating objects. It can bundle data with shared behavior together, which makes code simpler and more readable.

To declare a class in Dove, use the keyword class followed by an identifier, and a block {} containing all its member functions.

class Button {
    fun press() {
        print "You pressed the button!"
        print "This button has width " + self.width.to_string()
    }
}

Instance

To instantiate a class, we simply call the class by adding () after its idenfier, like a function call.

// This creates a Button instance
let button = Button()

An instance can contain an arbitrary number of fields, which is useful for storing data related to the instance. To access a field, we use the dot notation similar to most other OOP languages. Similarly, we can use this notation to set a field as well.

button.width = 10
print button.width // 10

Member Functions

We can also call its member functions after instantiating. Recall the method press defined above. Notice that we did not need to explicitly assign a press field to button, it was instead declared in the class Button.

button.press()
// "You pressed the button!"
// "This button has width 10"

The self in the member functions of a class refers to the instance of the class on which the function is being called. In this case, the self refers to button, whose width field was set to 10 earlier.

Initializers

The way above of initializing an instance is very error prone. What if we forgot to assign a value to the width field and tried calling button.press()? Accessing a field that does not exist will cause a runetime error. To solve this issue, we can create an initializer to the class by declaring a function called init.

class Button {
    fun init(width) {
        self.width = width
    }
    // ...
}

Notice that the initializer takes a parameter width and assign it to the width field of self. This ensure that every Buttoninstance created will have that field. To use this initializer, we instantiate the class like usual and pass thewidthargument. Theinit` method will be called and the necessary fields will be initialized.

let big_button = Button(20)
print big_button.width // 20