SoFunction
Updated on 2025-04-27

Detailed analysis of the function of importing underscores in Go language

Preface

In Go code, you sometimes see import statements similar to the following:

import _ "/mattn/go-sqlite3"

This underlines_The import method at the beginning seems a bit special, especially for novices, who may be confused. Why do you need to write this way? What does it do? Under what circumstances do you need to import with underscore? This article will analyze this issue in detail.

1. The basic function of underscore import

In Go,importStatements are used to import other packages to use the types, functions, constants, etc. of its exported content in the current package. Normally, we write this:

import "/mattn/go-sqlite3"

Then use the export content of the package in the code, for example:

db, err := ("sqlite3", ":memory:")

However, when we import a package, we want to execute the package'sinitFunctions, without directly using any exported content in the package, need to be imported using underscores. This way tells the Go compiler: whether I use this package directly or not, I need to compile it into the executable file and execute its initialization code.

2. Main uses of underline import

2.1 Initialize the package

In Go, each package can define ainitFunction, which will be automatically executed when the package is imported.initFunctions are usually used to initialize package-level variables, register plug-ins, load configuration files, or connect to external resources, etc.

For example, some database driver packages need to register themselves when the program starts, so thatdatabase/sqlPackages can recognize and use them. If the database driver package is not imported,The function will not be able to find the corresponding driver, causing the program to be unable to connect to the database.

For example:

Database driver package/mattn/go-sqlite3I will register myself when I am imported, and the following is the packageinitfunction:

func init() {
    ("sqlite3", &SQLiteDriver{})
}

Therefore, we need to import the package in our code, even if we don't use its export content directly. At this time, using underscore import is the right choice:

import _ "/mattn/go-sqlite3"

In this way, it is ensuredinitThe function is executed, thus completing the driver registration.

2.2 Ensure that the package is compiled into the executable file

Another scenario where underscore import is when a package's functionality needs to be used implicitly by other packages without directly referencing its export content in the current package. For example, some frameworks or libraries may need to import other packages to register plugins, load resources, or perform other initialization efforts.

For example, a web framework may require importing multiple template engine packages to support different template formats. At this time, although it is not necessary to use the template engine export content directly in the current package, they still need to be compiled into the executable file so that the framework can find and use them.

import _ "text/template"    // built-in template engine
import _ "/juju/amigo/template" // alternative template engine

Underscore import ensures that these packages are compiled into the final executable file, even if they are not directly referenced.

3. Things to note when importing underlines

While underscore import is very useful in some cases, there are some things to note:

  • Use only when initialization is requiredThe main purpose of underscore import is to execute packagesinitfunction. Underscore import is only required if the initialization logic of a certain package needs to be executed, but the export content of the package does not need to be directly used.

  • Avoid unnecessary importsUnnecessary underscore imports increase the volume of the final executable because the compiler compiles the package into the binary. Therefore, underscore import is only used if it is really needed.

  • Difference from normal importThe main difference between underscore import and ordinary import is that ordinary import will introduce the package name into the namespace of the current package, and you can directly use it to export the content, while underscore import will not introduce the package name, but will only execute the initialization logic of the package.

    import "/example/pkg"    // Normal import, you can directly use pkg to export contentimport _ "/example/another" // Underscore import, only another init function is executed

4. Summary

In summary, underscores are used in Go_The main purpose of package import is to execute the initialization logic of the package without directly using its export content. This method is very common in scenarios such as registering plug-ins, initializing database drivers, loading configuration files, etc.

The key point of underscore import is that it tells the Go compiler that even if the current package does not directly use the export content of the package, it needs to compile the package into the executable file and execute it.initfunction.

In actual development, underscore import can help us better manage initialization logic and reduce code redundancy, but we should also pay attention to avoid unnecessary use to keep the code concise and efficient.

This is the article about the function of importing underscores in Go language packages. For more related content on importing underscores in Go language packages, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!