Abstract Factory

package main

import (

        "fmt"

)

const (

        CircleID    = 0

        SquareID    = 1

        EllipseID   = 2

        RectangleID = 3

)

// ShapeFactory is an abstract factory for all shapes. It does not have any

// shape data on its own. Rather, it only produces the shape when the client

// provides the necessary shape data.

type ShapeFactory struct {

        Circle    []byte

        Square    []byte

        Ellipse   []byte

        Rectangle []byte

}

func (s *ShapeFactory) CreateCurvedShape(shape int) []byte {

        switch shape {

        case 0:

                return s.Circle

        case 2:

                return s.Ellipse

        default:

                return nil

        }

}

func (s *ShapeFactory) CreateStraightShape(shape int) []byte {

        switch shape {

        case 1:

                return s.Square

        case 3:

                return s.Rectangle

        default:

                return nil

        }

}

func main() {

        // client supplies the models to the factory

        s := &ShapeFactory{

                Circle: []byte("I'm a circle"),

                Square: []byte("I'm a square"),

        }

        // not all shapes are printed out since client only supply 2 out 4

        // concrete shape data.

        fmt.Printf("Circle: %v\n", s.CreateCurvedShape(CircleID))

        fmt.Printf("Square: %v\n", s.CreateStraightShape(SquareID))

        fmt.Printf("Ellipse: %v\n", s.CreateCurvedShape(EllipseID))

        fmt.Printf("Rectangle: %v\n", s.CreateStraightShape(RectangleID))

}