Module

Overview

Module is used to extend a class functionality. This is usually used for the common functionalities cross over a different kind of classes.

Basic Style

The module definition is basically below.

module M { 
    /* ... Defines a public method
        to extend a host class which this is mixined into. */
}

Mixin

The module is mixed into a class by mixin keyword.

class A {
    mixin M;
    /* ... */
}

mixin can have multiple modules like this.

class A {
    mixin M1, M2, M3;
    /* ... */
}

Extend a Class

By the module mixed into a class, the methods defined in the module are added to the class. For example, when the module M having the method of method1 is mixed into a class of A, A could have and use the method of method1. Note that the method of method1 must be a public method then.

module M {
    public method1() {
        System.println("This is a method1");
    }
}

class A {
    mixin M;
}

new A().method1();  // => This is a method1

Examples

Example 1. Normal case

Code

module M {
    public method1() {
        System.println("This is a method1");
    }
}

class A {
    mixin M;
}

new A().method1();  // => This is a method1

Result

This is a method1

Example 2. Add a common functionality

Code

module Printable {
    public print() {
        System.println("value = " + @value);
    }
}

class A {
    mixin Printable;
    @value = "'This is A.'";
}

class B {
    mixin Printable;
    @value = 256;
}

var a = new A();
var b = new B();
a.print();
b.print();

Result

value = 'This is A.'
value = 256

Example 3. Multiple mixin (1)

Code

module M1 {
    public method1() {
        System.println("This is a method1");
    }
}
module M2 {
    public method2() {
        System.println("This is a method2");
    }
}

class A {
    mixin M1, M2;
}

var a = new A();
a.method1();  // => This is a method1
a.method2();  // => This is a method2

Result

This is a method1
This is a method2

Example 4. Multiple mixin (2)

Code

module M0 {
    public method0() {
        System.println("This is a method0");
    }
}
module M1 {
    public method1() {
        System.println("This is a method1");
    }
}
module M2 {
    public method2() {
        System.println("This is a method2");
    }
}
module M3 {
    public method3() {
        System.println("This is a method3");
    }
}

class A {
    mixin M0;
    mixin M1, M2, M3;
}

var a = new A();
a.method0();  // => This is a method0
a.method1();  // => This is a method1
a.method2();  // => This is a method2
a.method3();  // => This is a method3

Result

This is a method0
This is a method1
This is a method2
This is a method3