Prototype Pattern
Prototype is a creational design pattern that allows cloning objects, even complex ones, without coupling to their specific classes.
All prototype classes should have a common interface that makes it possible to copy objects even if their concrete classes are unknown. Prototype objects can produce full copies since objects of the same class can access each other’s private fields.
Let’s try to figure out the Prototype pattern using an example based on the operating system’s file system. The OS file system is recursive: the folders contain files and folders, which may also include files and folders, and so on.
Each file and folder can be represented by an inode interface. inode interface also has the clone function.
Both file and folder structs implement the print and clone functions since they are of the inode type. Also, notice the clone function in both file and folder. The clone function in both of them returns a copy of the respective file or folder. During the cloning, we append the keyword “_clone” for the name field.
Demo
inode.go: Prototype interface
package main
type inode interface {
print(string)
clone() inode
}
file.go: Concrete prototype
package main
import "fmt"
type file struct {
name string
}
func (f *file) print(indentation string) {
fmt.Println(indentation + f.name)
}
func (f *file) clone() inode {
return &file{name: f.name + "_clone"}
}
folder.go: Concrete prototype
package main
import "fmt"
type folder struct {
children []inode
name string
}
func (f *folder) print(indentation string) {
fmt.Println(indentation + f.name)
for _, i := range f.children {
i.print(indentation + indentation)
}
}
func (f *folder) clone() inode {
cloneFolder := &folder{name: f.name + "_clone"}
var tempChildren []inode
for _, i := range f.children {
copy := i.clone()
tempChildren = append(tempChildren, copy)
}
cloneFolder.children = tempChildren
return cloneFolder
}
main.go: Client code
package main
import "fmt"
func main() {
file1 := &file{name: "File1"}
file2 := &file{name: "File2"}
file3 := &file{name: "File3"}
folder1 := &folder{
children: []inode{file1},
name: "Folder1",
}
folder2 := &folder{
children: []inode{folder1, file2, file3},
name: "Folder2",
}
fmt.Println("\nPrinting hierarchy for Folder2")
folder2.print(" ")
cloneFolder := folder2.clone()
fmt.Println("\nPrinting hierarchy for clone Folder")
cloneFolder.print(" ")
}
// output
Printing hierarchy for Folder2
Folder2
Folder1
File1
File2
File3
Printing hierarchy for clone Folder
Folder2_clone
Folder1_clone
File1_clone
File2_clone
File3_clone