去全局变量和短变量定义

Question

In the following snippet

package ...

var Conn *sql.DB // outer Conn

func Init(user, pwd, dbname string, port int) {
    Conn, err := sql.Open("postgres", "... args") // inner Conn
    // ..
}

the inner Conn is a new variable and outer Conn will remain null.

By explicitly defining err and replacing the short variable definition with assignment it seems to properly init the outer Conn variable

    var err error
    Conn, err = sql.Open("postgres", "... args") // inner Conn

Is there a simpler way to specify the inner Conn should not really be a scoped variable but instead the global Conn variable? I'm thinking something like package.Conn, but that's invalid inside the package itself.

Answer 1

Nope, that's it. := is just a shortcut to New() (https://golang.org/doc/effective_go.html#allocation_new) variable declaration (var foo int). A more idiomatic approach (and better design in general) is to return the connection and not to use global variables.

func Init(user string, pwd string, dbname string, port int) (*sql.DB, error) {
    // ...
}

Dependency injection is your friend, try not to break scope.