Basic concepts and common usage of golang reflection mechanism

Preface

Golang is a statically typed language, but it also provides a reflection mechanism so that the program can obtain the type information and structure information of the object at runtime and operate based on this information. In golang, reflection is used in many situations, such as dependency injection, json serialization, ORM, etc.

This article will introduce the basic concepts and common usage of golang reflection mechanism, and deepen understanding through some simple code examples. Hope readers can benefit from it.

Basic concepts of reflection mechanism

In golang, the core of the reflection mechanism is the reflect package. The reflect package provides multiple types and functions for reflecting the type information and structure information of objects at runtime. The following are some basic concepts:

• Type: Represents the type information of an object.
• Value: Represents the value information of an object.
• Kind: Represents the classification of an object type, such as int, string, map, etc.

Basic use of reflection mechanism

Get type information

In golang, use the reflect.TypeOf() function to obtain the type information of an object. The following is a simple example:

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var x float32 = 3.1415926
    fmt.Println("type:", reflect.TypeOf(x))
}

In this example, we define a variable x of type float32, and use the reflect.TypeOf() function to obtain its type information. The main function will output: type: float32.

Get value information

Use the reflect.ValueOf() function to obtain the value information of an object, for example:

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var x float32 = 3.1415926
    v := reflect.ValueOf(x)
    fmt.Println("value:", v)
}

In this example, we also define a float32 Type variable x, and use the reflect.ValueOf() function to obtain its value information. The main function will output: value: 3.1415925.

Modify value information

We can modify the value information of an object through reflection. First, we need to use the reflect.ValueOf() function to obtain the value information of an object. Then, use the reflect.Value method to modify the object's value. For example:

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var x float32 = 3.1415926
    v := reflect.ValueOf(&x)
    v.Elem().SetFloat(3.14)
    fmt.Println("x:", x)
}

In this example, we also define a float32 type variable x and use the reflect.ValueOf() function to obtain its value information. The key is that we pass a pointer to the variable x. Then, call the Elem() method on the value information to get the value pointed to by this pointer. Finally, we call the SetFloat() method to change the value of x to 3.14 and output the new value.

Get the method of the object

We can use the reflect.TypeOf() and reflect.ValueOf() functions to obtain the method information of the object. For example:

package main

import (
    "fmt"
    "reflect"
)

type User struct {
    Name string
    Age  int
}

func (u User) Describe() {
    fmt.Printf("Name:%s Age:%d\n", u.Name, u.Age)
}

func main() {
    u := User{"Bob", 18}
    v := reflect.ValueOf(u)

    fmt.Println("methods:")
    for i := 0; i < v.NumMethod(); i++ {
        fmt.Println(v.Method(i).Type())
    }
}

In this example, we define a structure named User and create a method named Describe(). In the main function, we create a User object u and use the reflect.ValueOf() function to obtain its value information. Then we loop through all methods and print their type information.

Summary

In this article, we briefly introduce the basic concepts and common usage of golang reflection mechanism, and provide some simple code examples to deepen understanding. In fact, the reflection mechanism can do more things, such as dynamically creating objects, determining whether two objects are equal, dynamically calling methods, etc. If you want to learn more about the reflection mechanism, it is recommended to read the official documentation and more advanced cases.

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