What is an interface? How to implement interface in golang?

Golang is a programming language loved by many programmers. It has excellent performance and powerful concurrency features. In Golang, interfaces are a very important and powerful feature. This article will introduce the implementation of Golang interface in detail.

1. What is an interface?

An interface is an abstract concept. It is a collection of methods that can be implemented by an object. In Golang, interfaces are defined through the keyword interface. An object is considered to implement this interface only if it implements all methods declared in the interface.

The following is an example:

type Greeter interface {
    Greet(greeting string) string
}

This interface contains a method Greet, which accepts a parameter of string type and returns a value of string type.

We can define a structure Cat and let it implement the Greeter interface:

type Cat struct{}

func (c Cat) Greet(greeting string) string {
    return "Meow"
}

StructureCat Implementation Greet method, so we can think that the Cat structure implements the Greeter interface. The implementation method of interface is a design pattern that separates concrete implementation and abstract type. This ensures code decoupling and flexibility.

2. Rules for interface implementation

When writing Golang programs, we need to follow some rules to implement the interface.

2.1 Interface implementation does not require explicit declaration

Unlike some other programming languages, Golang’s interface implementation is implicit. This means that if a type implements all methods in an interface, it automatically implements the interface.

2.2 An interface can only be assigned to a type that implements the interface

In Golang, an interface is a type, so it can be assigned like other types. Interface variables can be assigned to any type that implements the interface. However, only types that implement the interface can assign it to a declared interface variable. The following is an example:

type Greeter interface {
    Greet(greeting string) string
}

type Cat struct{}

func (c Cat) Greet(greeting string) string {
    return "Meow"
}

func main() {
    var g Greeter
    g = Cat{}
    g.Greet("Hello") // output: "Meow"
}

In this example, we assign an instance of the Cat type to the Greeter interface in the main function variable.

2.3 Interfaces can be nested

In Golang, interfaces can be nested. This means that one interface can contain another interface, creating more complex interfaces. The methods of the nested interface will also be included in the outer interface. Here is an example:

type Greeter interface {
    Greet(greeting string) string
}

type Helper interface {
    Help() string
}

type GreeterHelper interface {
    Greeter
    Helper
}

type Cat struct{}

func (c Cat) Greet(greeting string) string {
    return "Meow"
}

func (c Cat) Help() string {
    return "I am a cat"
}

func main() {
    var gh GreeterHelper
    gh = Cat{}
    gh.Greet("Hello") // output: "Meow"
    gh.Help()         // output: "I am a cat"
}

In this example, we declare a Helper interface that contains two methods and a Greeter interface that contains one method. Then we defined a GreeterHelper interface, which contains two interfaces, Greeter and Helper. Finally, we defined a Cat structure and made it implement both the Greeter and Helper interfaces. In the main function, we assign the Cat instance to the GreeterHelper interface variable, and then call Greet and Help respectively method.

3. Summary

Through the introduction of this article, we have learned about the implementation of the Golang interface and related rules. Interface is a very important feature in Golang and is often used in actual development. Being proficient in the use of interfaces can improve the scalability and reusability of code. It is one of the skills that every Golang programmer must master.

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