Let's talk about Golang reflection knowledge

Go language is a programming language launched by Google. It has the characteristics of concurrency, efficiency and maintainability, and is widely used in the modern Internet field. Reflection is a very important concept in the Go language, which allows the program to inspect and modify the values, types, and properties of variables at runtime. In this article, we will focus on introducing knowledge about Golang reflection.

1. What is reflection

Reflection refers to dynamically obtaining the type, value and method of variables when the program is running, and can be dynamically called and modified at runtime. In the Go language, each variable has a static type and value, and the reflection mechanism allows the program to obtain this information at runtime and use this information to perform necessary operations.

2. The use of reflection

In the Go language, the use of reflection is very extensive. For example: in JSON serialization and deserialization, objects need to be serialized into JSON strings or Deserialize JSON strings into objects; in the ORM framework, objects need to be mapped to table structures in relational databases; in RPC frameworks, dynamic checking and calling methods are required, etc.

In the Go language, the most important thing to use reflection is to obtain type information and value information. Using the Type type and Value type provided in the reflection library, you can obtain the type and value information of the variable.

3. Reflection Type

The Type type in the reflection library represents the type information of a variable, which can be obtained through reflect.TypeOf(). Generally, the Type type is an interface type, which contains information such as the underlying type of the variable, the package path, and whether it is a pointer type. The Type type has the following commonly used methods:

1. Name() string: Returns the name of the type.
2. String() string: The string representation of the return type, generally the same as the return value of the Name() method.
3. PkgPath() string: If the type is defined in a package, returns the path of the package, otherwise returns an empty string.
4. Kind() reflect.Kind: Returns the classification of the underlying type, that is, the specific type of the variable.

The reflect.Kind type in the reflection library represents the classification of the underlying type, which contains information such as basic types, composite types, and interface types. There are the following commonly used classifications:

1. reflect.Int
2. reflect.String
3. reflect.Bool
4. reflect.Array
5. reflect.Slice
6. reflect.Struct
7. reflect.Interface

Sample code:

type Person struct {
    Name string
    Age  int
}

func main() {
    var name string = "Tom"
    var age int = 18
    var p Person = Person{"Mike", 25}

    fmt.Println(reflect.TypeOf(name).Name(), reflect.TypeOf(name).Kind()) // string string
    fmt.Println(reflect.TypeOf(age).Name(), reflect.TypeOf(age).Kind())   // int int
    fmt.Println(reflect.TypeOf(p).Name(), reflect.TypeOf(p).Kind())       // Person struct
}

4. Reflection Value type

The Value type in the reflection library is used to obtain variables Value information can be obtained through reflect.ValueOf(). The Value type is also an interface type, including methods for obtaining and setting variable values, variable type information, and methods for operating on variables. The Value type has the following commonly used methods:

1. Kind() reflect.Kind: The specific type classification of the return value.
2. String() string: String representation of the return value.
3. Interface() interface{}: The interface type of the return value.
4. Type() reflect.Type: Returns the type information of the value.
5. CanSet() bool: Returns whether it can be set.
6. Set(): Set a value to a variable.

Sample code:

var name string = "Tom"
var age int = 18
fmt.Println(reflect.ValueOf(name).String()) // Tom
fmt.Println(reflect.ValueOf(age).Int())     // 18

5. Reflection method

The reflection library also provides a method similar to the calling method Call(), which can be used for dynamic calling Any method with a known signature, where the signature specifies the method name, parameter types, and return value type. When calling a method, you need to provide a method object and a set of parameter values. The reflection library will dynamically call the corresponding method based on the method signature and the passed parameter list.

Sample code:

type Person struct {
    Name string
    Age  int
}

func (p Person) SayHello() {
    fmt.Printf("Hello, I'm %s, age %d.\n", p.Name, p.Age)
}

func main() {
    var p Person = Person{"Mike", 25}
    v := reflect.ValueOf(p)
    m := v.MethodByName("SayHello")
    m.Call(nil)
}

6. Limitations of reflection

Although the reflection library provides a wealth of methods to dynamically obtain and modify variable information, during the reflection operation Some exceptions may be thrown, such as: the type of the variable does not support a method, accessing an undisclosed field, illegal type conversion, etc. In addition, the reflection mechanism will also lead to a decrease in program running efficiency, because when dynamically obtaining and modifying variable information, some additional operations such as type conversion, memory allocation, and method calling are required, which has a negative impact on the performance of the program.

7. Summary

Reflection is a very important concept in the Go language. Through the reflection mechanism, information such as the type, value, and attributes of variables can be obtained and modified at runtime. In actual programming, we can use the reflection mechanism to implement some advanced features, such as dynamically creating objects, accessing undisclosed fields, dynamically calling methods, etc. However, you need to pay attention to some limitations when using the reflection mechanism, and try to avoid performance degradation while ensuring the correctness of the program.

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