What Does an Underscore in a Go Import Statement Mean?

Underscore in Import Statements: Exploring Side-Effects

In programming, an underscore in front of an import statement serves a specific purpose. Consider this code snippet from go-sqlite3:

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

Here, the underscore in front of the import statement for "github.com/mattn/go-sqlite3" raises the question: What does it mean?

Meaning and Purpose

The underscore in an import statement signifies importing a package solely for its side-effects, without importing its functions or variables. According to the Go Specification:

To import a package solely for its side-effects (initialization), use the blank identifier as explicit package name:
import _ "lib/math"

In the Context of go-sqlite3

In the case of go-sqlite3, the underscore import has a specific side-effect. It registers the sqlite3 driver as a database driver. This is done within the package's init() function, which is executed during package initialization.

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

Registering the driver allows you to use sqlite3 with the standard library's sql interface:

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

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