History and context

Go is a compiled program language created by Google in 2009.

It has similarities with C and Java, but also with Python. Unlike Java, it does not require you to create a class in order to code an application.

Many developers call this language golang instead of simply Go. Because there is another programming language called Go! (with exclamation mark) created in 2003 by Francis McCabe and Keith Clark.

Why another programming language?

Well, there are several explanations for this, but Golang’s main differential is that it’s a compiled language, focused on productivity, unlike other compiled languages like C++. Since most modern programming languages are interpreted (even those based on Virtual Machines), having a compiled programming language, with modern syntax, is an advantage for developers.

Another reason is that it has resources for [concurrent programming] (https://en.wikipedia.org/wiki/Concurrent_computing).

Wikipedia has an excellent answer to this question:

Go was designed at Google in 2007 to improve programming productivity in an era of multicore, networked machines and large codebases. The designers wanted to address criticism of other languages in use at Google, but keep their useful characteristics:

- Static typing and run-time efficiency (like C++);
- Readability and usability (like Python or JavaScript);
- High-performance networking and multiprocessing;
- The designers were primarily motivated by their shared dislike of C++.

Free sample

Let’s start? Learning a new language is very stressful, so let’s avoid too many details early on. There is a shortcut that I really like: MyCompiler.io.

It’s a kind of online IDE, which allows us to create and execute code in many languages, including golang. I recommend that you sign up and log in to save your code. Then choose Go and type the program start.go.

package main

import (
	"fmt"
	"time"
)

func main() {

	timeNow := time.Now()
	fmt.Println("Current time: ", timeNow.String())
}

Enter this program on MyCompiler and run:

One píece at a time

Every golang program has the same structure: Package declaration, imports and main function. And that is exactly how our program is divided.

First we declare a package called main. It could be another name, if we wanted to create a function library, but as my goal is to create an executable program, I have to put it inside a main package (we’ll see this later).

package main

Then I can import code from other packages, similar to what we do in Java or Python. I’m importing two packages from the golang Standard Library: fmt and time.

import (
	"fmt"
	"time"
)

Finally, I create a function called main and, inside its body, I put the commands I want to execute:

func main() {

	timeNow := time.Now()
	fmt.Println("Current time: ", timeNow.String())
}

Ok. How is this code executed? In golang every package called main generates an executable, and must have a function called main. For example, try renaming the function to see what happens…

runtime.main_main·f: function main is undeclared in the main package

Challenge

Modify the program to display the date in Brazilian format: dd/mm/aaaa hh:mm:ss. (Tip: https://golang.org/pkg/time/#Time.Format).