golang parameter modification

Golang is an open source programming language originally developed by Google. Its main features include: efficient concurrency, concise syntax, and excellent performance. Among them, functions are a very basic part of Golang programming, and function parameters are also a core concept in Golang. In a function, we can modify the value of a parameter. This behavior is called parameter modification. In this article, we will introduce parameter modification in Golang in detail.

1. Parameter passing method in Golang

In other programming languages, common parameter passing methods include: value passing and reference passing. In value transfer, the function's modification of the parameters will not affect the variables when the function is called. In reference passing, the function's modification of the parameters will affect the variables when the function is called.

In Golang, the parameter passing method is similar to reference passing, but parameter passing in Golang does not entirely use pointers. The parameter passing method in Golang is called pass by value, that is, the value of the variable itself is passed, but when modified inside the function, the value at the address of the variable is operated.

2. Parameter modification in Golang

In Golang, parameters in functions can be divided into two types: value-passing types and reference-passing types. When a value type parameter is executed, a copy of the parameter value will be copied and then operated inside the function, but this will not affect the value of the original variable passed in when the function is called. When passing reference type parameters, when the function is executed, the address of the parameter will be passed into the function, and the value of the original variable will be directly manipulated through the address, so modifications in the function will affect the value of the original variable.

The parameter passing method in Golang allows us to easily modify parameters. For example, we define a string variable, pass it into the function as a parameter, modify the value of the string variable in the function, and then output the modified value in the main function. The code is as follows:

package main

import "fmt"

func changeStr(str string) {
    str = "hello"
}

func changeStrPtr(str *string) {
    *str = "hello"
}

func main() {
    str := "world"
    changeStr(str)
    fmt.Println(str) // 输出 world

    changeStrPtr(&str)
    fmt.Println(str) // 输出 hello
}

In the above code, we define two functions changeStr and changeStrPtr, which are used to modify the string variable str respectively. In the changeStr function, we just assign the passed string variable to "hello", but this modification will not affect the str variable in the main function. In the changeStrPtr function, we modify the value pointed by the passed parameter pointer to "hello". This modification will directly affect the str variable in the main function.

3. Modification of value type parameters in Golang

For value type parameters, modifications in the function will not affect the variables when the function is called. This is because the function makes a copy of the value type parameter and then modifies it inside the function. Therefore, when we modify the value type parameters in the function, we are only modifying the copy of the parameters and have no effect on the original variables.

package main

import "fmt"

func changeInt(i int) {
    i = 10
    fmt.Println("i in function:", i)
}

func main() {
    i := 5
    changeInt(i)
    fmt.Println("i in main:", i)
}

In the above code, we define a function changeInt, which receives the parameter i of type int and sets the value of i to 10. In the main function, we define a variable i of type int and set its value to 5. Then, we call the changeInt function, passing i as a parameter. When the function is executed, we output the value of i in the main function. Since we modified the copy of parameter i in the changeInt function, the value of i after the function is executed is still 5.

4. Modification of reference type parameters in Golang

For reference type parameters, modifications in the function can directly affect the variables when the function is called. In Golang, pointer type is a reference type. If the parameter we pass in a function is of pointer type, modifying the value pointed to by the pointer inside the function will directly affect the variable when the function is called.

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

func changePerson(p *Person) {
    p.Name = "Tom"
    p.Age = 18
    fmt.Println("Person in function:", p)
}

func main() {
    person := Person{Name: "Jack", Age: 20}
    changePerson(&person)
    fmt.Println("Person in main:", person)
}

In the above code, we define a structure named Person, which contains two fields: Name and Age. We also define a function changePerson, which receives a pointer to the Person structure type. Inside the function, we modify the value pointed to by the pointer and output the modified Person structure. In the main function, we define a Person variable person and initialize it to {Name: "Jack", Age: 20}. Next, we pass the person pointer as a parameter to the changePerson function. When the function is executed, we output the value of person in the main function, and we can find that person has been modified to {Name: "Tom", Age: 18}.

5. Notes

You need to pay attention to the following points when using parameter modification:

1. You need to know how to pass parameters, value type parameters and reference type parameters. The modification methods are different, so be careful not to confuse them.
2. If the parameter received by the function is a variable that already has a value in the main function, then its address needs to be passed as a parameter when calling the function, otherwise the function cannot modify the variable.
3. When modifying parameters inside a function, it is best to add security verification to avoid unnecessary impact on the original variables.

6. Summary

This article introduces parameter modification in Golang, including parameter passing methods and modification methods of value type parameters and reference type parameters. In a function, we can modify the value of the original variable by modifying the parameters, but we need to pay attention to the passing method of parameters and the reasonable use of modification methods. Modifying parameters can not only improve the efficiency of the program, but also allow us to more flexibly control the execution of the program during programming.

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