Boo Primer: [Part 09] Methods

Added by Cameron Kenneth Knight

Definition: Method - A function exclusively associated with a class.

Defining a Method

Methods must be defined in classes. They are declared just like functions are.

method example

class Cat:
    def Roar():
        print "Meow!"

cat = Cat()
cat.Roar()

// Output: Meow!

An object of Cat must be instanced, then its methods can be called.

Recommendation: Names of methods should always be verbs. They should also be declared in PascalCase.

Class Constructor and Destructor

Constructors and Destructors are special methods that are called on when a class is being instanced or destroyed, respectively. Both are optional.

Constructor and Destructor example

class Cat:
    def constructor():
        _name = 'Whiskers'

    def destructor():
        print "$_name is no more... RIP"

    [Getter(Name)]
    _name as string

cat = Cat()
print cat.Name

// Output:
// Whiskers
// Whiskers is no more... RIP

If a constructor has arguments, then they must be supplied when instancing. Destructors cannot have arguments.

Constructor and Destructor example

class Cat:
    def constructor(name as string):
        _name = name

    [Getter(Name)]
    _name as string

cat = Cat("Buttons")
print cat.Name

// Output: Buttons

Be Careful: Do not depend on the destructor to always be called.

Method Modifiers

Modifier	Description
abstract	an abstract method has no implementation, which requires that an inheriting class implements it.
static	a static method is common to the entire class, which means that it can be called without ownership of a single instance of the class
virtual	See Part 10 - Polymorphism, or Inherited Methods
override	See Part 10 - Polymorphism, or Inherited Methods

All these modifiers also apply to properties (If they are explicitly declared).

static can also apply to fields.

static example

class Animal:
    def constructor():
        _currentId += 1
        _id = _currentId

    [Getter(Id)]
    _id as int

    static _currentId = 0

This will cause the Id to increase whenever an Animal is instanced, giving each Animal their own, unique Id.

All the methods defined in an interface are automatically declared abstract.

Abstract methods in a class must have a blank code block in its declaration.

abstract example

class Feline:
    abstract def Eat():
        pass

interface IFeline:
    def Eat()

Both declare roughly the same thing.

Member Visibility

Visibility Level	Description
public	Member is fully accessible to all types.
protected	Member is only visible to this class and inheriting classes.
private	Member is only visible to this class.
internal	Member is only visible to classes in the same assembly.

Important Information: All fields are by default protected. All methods, properties, and events are by default public.

Recommendation

Fields are typically either protected or private. Usually instead of making a public field, you might make a public property that wraps access to the field instead. This allows subclasses to possibly override behavior.

Methods can have any visibility.

Properties can have any visibility, and typically have both a getter and a setter, or only a getter. Instead of a set only property, consider using a method instead (like "SetSomeValue(val as int)").

Recommendation: It is recommended you prefix field names with an underscore if it is a private field.

Declaring Properties in the Constructor

One very nice feature that boo offers is being able to declare the values of properties while they are being instanced.

class Box:
    def constructor():
        pass

    [Property(Value)]
    _value as object

box = Box(Value: 42)
print box.Value

// Output: 42

The constructor didn't take any arguments, yet the Value: 42 bit declared Value to be 42, all in a tighly compact, but highly readable space.

Exercises

1. Create two classes, Predator and Prey. To the Predator class, add an Eat method that eats the Prey. Do not let the Prey be eaten twice.

Go on to Part 10 - Polymorphism, or Inherited Methods

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