Underscore imports

In go you can use an underscore (_) for variables or function return values that you want to ignore. The same syntax can be applied to import statements. eg.

import (
	"database/sql"
	_ "github.com/go-sql-driver/mysql"
)

What’s the point of importing something and ignoring it? Because you want access to side effects via the init() function in the package.

Why we import SQL drivers as the blank identifier ( _ ) in Go

The above article explains the situation well, but the basic gist in this example is that the database/sql package contains general code but no implementation for any specific database engine. The init() function in the mysql package registers itself as a concrete implementation of the database code.

Following on from that, this question explains where init() fits into the sequence of execution.

When is the init() function run?

This image from one of the answers shows with great clarity the sequence of things that get executed before the main() function.

I mentioned databases above, but this pattern can be used in many other circumstances eg. image processing libraries.