Programming

My First Package

One first Go form to keep our code DRY are functions, second one, packages.

This chapter is about creating our first package so we can reuse it from any other Go program in our system.

Code organization

We are going to use the same hello world program but exporting it to an independente package.

    ~(gomix) tree -L 2 .
    .
    ├── bin
    ├── pkg
    │   └── linux_amd64
    └── src
        └── hello
            └── main.go

Our executable code

    package main                                                                                              

    import (                                                                                                  
       "fmt"                                                                                                  
       hello "hello/hello"                                                                                    
      )                                                                                                       

    func main() {                                                                                             
      fmt.Println(hello.SayHello())                                                                           
    }  

1. import: we will import a package under the same tree with the same name hello.
2. We have replace the string to be printed in our main function with a function call imported from the hello packg: SayHello().

Our Package, the where

In the same directory of our hello project, lets create a new subdirectory called hello with the folllowing source code in the source file hello.go:

    ├── hello
        ├── hello
        │   └── hello.go
        └── main.go

We have a simple design, main, the binary loads hello package in order to call an exported function in it to achieve the same result of the original program. The benefit, any other Go program could use it.

Our Package, the code

    package hello                                                                                             
    func SayHello() string {                                                                                  
      return("Hello Go Gomix@Fedora, 世界")                                                                   
    } 

1. First line we declared the name of our package: hello
2. We have create a simple function SayHello.
   • The first letter in the name must be uppercase in order to be exported. expuesta al exterior.

Package building and installation

    $ go install hello/hello
    $ tree -L 3 pkg/
    pkg/
    └── linux_amd64
        ├── github.com
        ├── gochess-00
        │   └── hello.a
        ├── golang.org
        │   └── x
        └── hello
            └── hello.a     <- pkg compiled

Sample run output

    $ go run src/hello/main.go 
    Hello Go Gomix@Fedora, 世界

Voilá!

Even i did simplified a lot, i think you have a base ground from where to start and move forward creating your own Go packages and reuse them effectivelly following one of the major mantras of software development: reuse the code, DRY.