Golang function method type assertion usage method

Golang is an efficient programming language that is currently popular because of its simplicity, efficiency and reliability. Function and method type assertions in Golang are one of the important tools commonly used by advanced programmers. Through this article, we will delve into the use of method type assertions for Golang functions.

1. Introduction to method type assertion

In Golang, method type assertion is the type conversion between pointers and values. By using dot notation to call methods, Golang is doing something behind the scenes. When you call a method, you actually pass the receiver (for values ​​and pointers) to the method. Using method type assertions, we can freely convert between values ​​and pointers.

For example:

type MyType struct {
    field int
}

func (mt MyType) sayHi() {
    fmt.Println("Hi from MyType with field:", mt.field)
}

func (mt *MyType) sayBye() {
    fmt.Println("Bye from MyType with field:", mt.field)
}

mt := &MyType{field: 42}
mt.sayHi() // Hi from MyType with field: 42

var i interface{} = mt
i.(MyType).sayHi() // Hi from MyType with field: 42

i.(MyType).sayBye() // 运行时error：invalid type assertion: i.(MyType) (non-interface type *interface {} on left)

2. Pointer type and value type

In Golang, a structure can be a value type or a pointer type. A structure of pointer type can change its state in a method, while a structure of value type does not change its state.

Pointer type MyType:

type MyType struct {
    field int
}

func (mt *MyType) sayHi() {
    fmt.Println("Hi from MyType with field:", mt.field)
}

mt := &MyType{field: 42}
mt.sayHi() // Hi from MyType with field: 42

Value type MyType:

type MyType struct {
    field int
}

func (mt MyType) sayHi() {
    fmt.Println("Hi from MyType with field:", mt.field)
}

mt := MyType{field: 42}
mt.sayHi() // Hi from MyType with field: 42

3. Use of method type assertion

In Golang, method Type assertions can help us master conversions between pointer types and value types. In the following example, we demonstrate how to use method type assertions.

type MyType struct {
    field int
}

func (mt MyType) sayHi() {
    fmt.Println("Hi from MyType with field:", mt.field)
}

func (mt *MyType) sayBye() {
    fmt.Println("Bye from MyType with field:", mt.field)
}

func main() {
    mt := &MyType{field: 42}
    mt.sayHi() // Hi from MyType with field: 42

    // 方法类型断言：值类型转换成指针类型
    var imt interface{} = MyType{field: 24}
    p, ok := imt.(*MyType) // ok 变量用于检查类型断言是否成功
    if ok {
        p.sayHi() // Hi from MyType with field: 24
    } else {
        fmt.Println("assertion failed")
    }

    // 方法类型断言：指针类型转换成值类型
    imt = mt
    v, ok := imt.(MyType) // ok 变量用于检查类型断言是否成功
    if ok {
        v.sayHi() // Hi from MyType with field: 42
    } else {
        fmt.Println("assertion failed")
    }
}

Using method type assertions allows us to freely convert between values ​​and pointers, thereby simplifying the programming process.

4. Summary

In Golang, method type assertion is one of the important tools commonly used by advanced programmers. With method type assertions, we can freely convert between values ​​and pointers, thus simplifying the programming process. This article details the difference between pointer types and value types, and how to use method type assertions. For beginners, method type assertions can be a bit complicated, but as you gain experience, understanding and mastering method type assertions will be of great benefit.

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