Golang package settings

Golang is an efficient, concise, and safe programming language that is popular for its excellent concurrency performance, simple syntax, and readability. In Golang, a package is the basic unit for organizing code, and each package can contain multiple files.

This article will introduce how to set up Golang packages, including important concepts such as package names, import paths, visibility, version control, and documentation comments.

1. Package name

In Golang, every file must belong to a package. A Golang package consists of one or more files with the .go suffix. Package names must be unique and consistent with their directory names.

Example:

Suppose we wrote the following code in a directory named hello:

package main

import "fmt"

func main() {
    fmt.Println("Hello, World!")
}

Open a terminal in the directory and execute the following command:

go run .

will output Hello, World!. In this example, we used the package name main because the directory name of the package is hello and the package does not belong to any other package.

2. Import path

In Golang, use the import keyword to import one or more packages. The import path can be a relative path or an absolute path.

Relative path:

Suppose we wrote the following code in the src/hello directory:

package main

import "./utils"

func main() {
    utils.PrintMessage("Hello")
}

Open a terminal in this directory and execute the following command:

go run .

Hello will be output. In this example, we use a relative path to import the package named utils.

Absolute path:

Suppose we wrote the following code in the $GOPATH/src/example.com/hello directory:

package main

import "example.com/utils"

func main() {
    utils.PrintMessage("Hello")
}

Open the terminal in this directory and execute The following command:

go run .

will output Hello. In this example, we imported the package named utils using an absolute path. Note that example.com is a virtual domain name, which will be mapped to the $GOPATH/src/example.com directory.

3. Visibility

In Golang, identifiers such as variables, constants, functions, and structures have different visibility. The visibility of an identifier depends on the package in which it exists.

In a package, identifiers can be public or private. An identifier is only visible within the package in which it appears.

All identifiers starting with uppercase letters are public and they can be used by other packages; all identifiers starting with lowercase letters are private and they can only be used within the package in which they are located.

For example, a package named utils might contain the following code:

package utils

import "fmt"

const Pi = 3.14159

func add(x int, y int) int {
    return x + y
}

func PrintMessage(message string) {
    fmt.Println(message)
}

When the package is used in other packages, only the public identifier can be accessed:

package main

import (
    "example.com/utils"
    "fmt"
)

func main() {
    fmt.Println(utils.Pi)
    utils.PrintMessage("Hello")
}

Open a terminal in the directory and execute the following command:

go run .

will output 3.14159 and Hello.

4. Version Control

In Golang, use the go.mod file for version management. The go.mod file defines the name, version information and dependency information of the current module.

Suppose we want to use a third-party package named utils in the hello project. We can use the following command to add it to the dependency list:

go get example.com/utils@v1.0.0

This command will download the package named utils Third-party package version v1.0.0 and add it to the dependency list. In the go.mod file, the following content will be added:

module example.com/hello

go 1.16

require example.com/utils v1.0.0

When using a third-party package in the code, you can directly import its package name, for example:

package main

import (
    "example.com/utils"
    "fmt"
)

func main() {
    fmt.Println(utils.Pi)
    utils.PrintMessage("Hello")
}

5. Documentation comments

In Golang, use documentation comments to generate documentation and improve code readability. Documentation comments start with // or / / and precede the identifier. When generating documentation using the godoc tool, they will be parsed into documentation.

For example, the following is an example of a function with documentation comments:

package utils

// add 函数计算两个整数的和。
func add(x int, y int) int {
    return x + y
}

When using the godoc tool to generate documentation, the following content will be displayed:

FUNCTIONS

func add(x int, y int) int
    add 函数计算两个整数的和。

Summary

This article introduces the basic concepts of Golang package settings, including package name, import path, visibility, version control and documentation comments, etc. These concepts are the basic knowledge for organizing code using Golang. Mastering them can make your Golang code more standardized, easier to maintain and expand.

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