Bridge Pattern in Go

The Bridge pattern is a structural design pattern that decouples an abstraction from its implementation so that the two can vary independently. This pattern involves an interface acting as a bridge which makes the functionality of concrete classes independent from interface implementer classes. Both types of classes can be altered structurally without affecting each other.

In this Go code, the Bridge pattern is implemented using PrinterAPI as the bridge interface, PrinterAPI1 and PrinterAPI2 as the concrete implementer classes, and NormalPrinter and PacktPrinter as the abstraction classes.

Code Explanation

PrinterAPI interface

This is the bridge implementer interface. It has a method PrintMessage(string) error.

PrinterAPI1 and PrinterAPI2

These are the concrete implementers of the PrinterAPI interface. PrinterAPI1 uses the standard output to print the message while PrinterAPI2 uses an io.Writer to print the message. If the Writer in PrinterAPI2 is not set, it returns an error.

PrinterAbstraction Interface

This is the abstraction interface. It has a method Print() error.

NormalPrinter and PacktPrinter

These are the concrete implementers of the PrinterAbstraction interface. They use a PrinterAPI to print a message. NormalPrinter prints the message as is, while PacktPrinter adds a prefix to the message.

Usage

You can use the NormalPrinter or PacktPrinter to print a message. You need to provide a PrinterAPI (either PrinterAPI1 or PrinterAPI2) to these printers. If you use PrinterAPI2, you also need to provide an io.Writer.

printer := &NormalPrinter{
    Msg:     "Hello, World!",
    Printer: &PrinterAPI1{},
}
err := printer.Print()
if err != nil {
    log.Fatal(err)
}

This pattern allows you to change the way the message is printed (by switching between PrinterAPI1 and PrinterAPI2) without changing the printer classes (NormalPrinter and PacktPrinter). Similarly, you can change the printer classes without affecting the PrinterAPI classes.