How to share variables through packages

I'm trying to figure out how can I return a value from a function in a file of a package name to another package. for example let's assume you have

package main

func main(){
   x := 5
   a := res.Test(x)
}

package res

func Test(x int) (y int){
    y := x*2
    return y
}

If I compile it I would get an error: res.Test used as value. Where am I doing wrong, how can I return y to the main/ and other package? thx

Solution

At its most basic, a Go packages must be in their own file directory. res goes into ~/go/src/res/.

// ~/go/src/res/res.go
package res

func Test(x int) (y int){
    // Note that y is already declared.
    y = x*2
    return y
}

Then your main.go can import this package.

package main

import(
    "res"
    "fmt"
);

func main(){
   x := 5
   a := res.Test(x)
   fmt.Println(a)
}