implement abstract factory pattern

creational/abstract-factory.md

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+# Abstract Factory Pattern
+
+The abstract factory pattern provides a way to encapsulate a group of individual factories 
+that have a common theme without specifying their concrete classes.
+
+## Implementation
+
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+type AbstractFactory interface {
+	CreateProductA() AbstractProductA
+	CreateProductB() AbstractProductB
+}
+
+type ConcreteFactory1 struct {
+}
+
+func NewConcreteFactory1() *ConcreteFactory1 {
+	return &ConcreteFactory1{}
+}
+
+func (ConcreteFactory1) CreateProductA() AbstractProductA {
+	return NewConcreteProductA1()
+}
+
+func (ConcreteFactory1) CreateProductB() AbstractProductB {
+	return NewConcreteProductB1()
+}
+
+type ConcreteFactory2 struct {
+}
+
+func NewConcreteFactory2() *ConcreteFactory2 {
+	return &ConcreteFactory2{}
+}
+
+func (ConcreteFactory2) CreateProductA() AbstractProductA {
+	return NewConcreteProductA2()
+}
+
+func (ConcreteFactory2) CreateProductB() AbstractProductB {
+	return NewConcreteProductB2()
+}
+
+type AbstractProductA interface {
+	UsefulFunctionA() string
+}
+
+type AbstractProductB interface {
+	UsefulFunctionB() string
+	AnotherUsefulFunctionB(collaborator AbstractProductA) string
+}
+
+type ConcreteProductA1 struct {
+}
+
+func NewConcreteProductA1() *ConcreteProductA1 {
+	return &ConcreteProductA1{}
+}
+
+func (ConcreteProductA1) UsefulFunctionA() string {
+	return "The result of the product A2."
+}
+
+type ConcreteProductA2 struct {
+}
+
+func NewConcreteProductA2() *ConcreteProductA2 {
+	return &ConcreteProductA2{}
+}
+
+func (ConcreteProductA2) UsefulFunctionA() string {
+	return "The result of the product A2."
+}
+
+type ConcreteProductB1 struct {
+}
+
+func NewConcreteProductB1() *ConcreteProductB1 {
+	return &ConcreteProductB1{}
+}
+
+func (ConcreteProductB1) UsefulFunctionB() string {
+	return "The result of the product B1."
+}
+
+func (ConcreteProductB1) AnotherUsefulFunctionB(collaborator AbstractProductA) string {
+	return "The result of the product B2."
+}
+
+type ConcreteProductB2 struct {
+}
+
+func NewConcreteProductB2() *ConcreteProductB2 {
+	return &ConcreteProductB2{}
+}
+
+func (ConcreteProductB2) UsefulFunctionB() string {
+	return "The result of the product B2."
+}
+
+func (ConcreteProductB2) AnotherUsefulFunctionB(collaborator AbstractProductA) string {
+	result := collaborator.UsefulFunctionA()
+	return fmt.Sprintf("The result of the B2 collaborating with the (%s)", result)
+}
+```
+
+## Usage
+
+```go
+
+func clientCode(factory AbstractFactory) {
+	productA := factory.CreateProductA()
+	productB := factory.CreateProductB()
+	fmt.Println(productB.UsefulFunctionB())
+	fmt.Println(productB.AnotherUsefulFunctionB(productA))
+}
+
+func main() {
+	fmt.Println("Client: Testing client code with the first factory type:")
+	clientCode(NewConcreteFactory1())
+
+	fmt.Println()
+
+	fmt.Println("Client: Testing the same client code with the second factory type:")
+	clientCode(NewConcreteFactory2())
+}
+```