What does an underscore in front of an import statement mean?

Question

I saw this example from sqlite3 on GitHub :

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


        

Answer 1

While other answers described it completely, for "Show me The Code" people, this basically means: create package-level variables and execute the init function of that package.

And (if any) the hierarchy of package-level variables & init functions of packages that, this package has imported.

The only side effect that a package can make, without being actually called, is by creating package-level variables (public or private) and inside it's init function.

Note: There is a trick to run a function before even init function. We can use package level variables for this by initializing them using that function.

func theVeryFirstFunction() int {
    log.Println("theVeryFirstFunction")
    return 6
}

var (
    Num = theVeryFirstFunction()
)

func init() { log.Println("init", Num) }