When Should You Import Go Packages for Side Effects Only?

Importing Packages for Side-Effects in Go

The Go programming language allows you to import packages solely for their side-effects, such as initializing external resources. This is achieved by using the blank identifier as the package name.

Use Case: Database Driver Initialization

One practical use case for importing with a blank identifier is when initializing database drivers. For example, suppose you want to use the github.com/mattn/go-sqlite3 driver in your Go program. You can achieve this without explicitly using any of the driver's exported functions by importing it with the following syntax:

import _ "github.com/mattn/go-sqlite3"

This import statement triggers the initialization of the go-sqlite3 driver. The driver's init function, defined as follows:

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

gets executed when the package is imported. This function registers the sqlite3 driver with the sql package, making it available for use by your program.

How It Works

The import with a blank identifier works because of the init function. Each source file in a Go package can define its own init function, which is executed before any other code in the package. This allows for initialization of external resources without requiring explicit function calls.

When a package is imported with a blank identifier, its init function is still executed. This allows for side-effects such as resource initialization without introducing unnecessary variables or functions into the importing package's namespace.

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