go pakcages

package is a collection of source files begining with "package nameofpackage".

import "fmt"
// now useable fmt outputs
fmt.Print(...)

import my "fmt"  // with my own name. (for purpose if namespace coliders ;)
my.Print(...)

each package can have an init() for initalization data (single threaded).

let see:
a.go

package a

import "fmt"

var A int

func init() {
    A = 4;
  fmt.Print("A init\n");
}

b.go

package b

import "fmt"

var B int

func init() {
  B=15;
  fmt.Print("B init\n");
}

mainab.go

package main

import (
  "fmt";
  "./a";
  "./b";
)

func main() {
  fmt.Print("call main()\n");
  var x= a.A;
  var y= b.B;
  var z = x + y;
  fmt.Print(z);
}

output:

./6.out 
B init
A init
call main()

at first there will be called init. later the main.

"To build a program, the packages, and the files within them, must be compiled in the correct order.
Package dependencies determine the order in which to build packages. "