The Decorator Pattern is a design pattern that allows behavior to be added to an individual object, dynamically, without affecting the behavior of other objects from the same class.
The “Gang of Four” patterns book describes the Decorator Pattern as “attaching additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.”
Example
In Golang, the Decorator Pattern can be implemented using interfaces and anonymous functions. Let’s see a code example:
package main
import "fmt"
type Printer interface {
Print() string
}
type SimplePrinter struct {}
func (sp *SimplePrinter) Print() string {
return "Hello, world!"
}
func BoldDecorator(p Printer) Printer {
return PrinterFunc(func() string {
return "<b>" + p.Print() + "</b>"
})
}
type PrinterFunc func() string
func (pf PrinterFunc) Print() string {
return pf()
}
func main() {
simplePrinter := &SimplePrinter{}
boldPrinter := BoldDecorator(simplePrinter)
fmt.Println(simplePrinter.Print()) // Output: Hello, world!
fmt.Println(boldPrinter.Print()) // Output: <b>Hello, world!</b>
}In the code example above, we declare a Printer interface and a SimplePrinter struct that implements the Print() method.
