Understanding Underscore Import Statements

In the world of Go programming, the underscore character ( _ ) preceding an import statement holds a specific significance. Let's explore its meaning and usage.

The Purpose of Underscore Imports

The underscore (_ ) in an import statement indicates that the package is imported solely for its side effects. It does not import any functions, methods, or variables from the package.

Side Effects in Go Packages

Some Go packages have initialization functions (typically named init() ) that perform actions when the package is imported. These actions can include registering custom database drivers, initializing global variables, or configuring logging.

Underscore Import for Side Effects

To import a package for its side effects and nothing else, the underscore identifier is used as an explicit package name in the import statement. For example, consider the code snippet from go-sqlite3:

import (
    "database/sql"
    "fmt"
    _ "github.com/mattn/go-sqlite3"
    "log"
    "os"
)

In this case, the underscore import of "github.com/mattn/go-sqlite3" registers the sqlite3 driver with the standard sql library. This enables you to use sqlite3 as a database connection in your code without needing to import any functions from that package.

Registering SQLite3 Driver

In the case of go-sqlite3, the following initialization code is executed when the package is imported:

sql.Register("sqlite3", &SQLiteDriver{})

This registration allows you to use sqlite3 like this:

db, err := sql.Open("sqlite3", "./foo.db")

Conclusion

Underscore import statements in Go are a convenient way to import a package solely for its side effects. They allow you to take advantage of package initialization routines without explicitly importing functions or variables. By understanding the purpose and usage of underscore imports, you can effectively manage package dependencies and side effects in your Go projects.