Book Image

Mastering Go - Second Edition

By : Mihalis Tsoukalos
Book Image

Mastering Go - Second Edition

By: Mihalis Tsoukalos

Overview of this book

Often referred to (incorrectly) as Golang, Go is the high-performance systems language of the future. Mastering Go, Second Edition helps you become a productive expert Go programmer, building and improving on the groundbreaking first edition. Mastering Go, Second Edition shows how to put Go to work on real production systems. For programmers who already know the Go language basics, this book provides examples, patterns, and clear explanations to help you deeply understand Go’s capabilities and apply them in your programming work. The book covers the nuances of Go, with in-depth guides on types and structures, packages, concurrency, network programming, compiler design, optimization, and more. Each chapter ends with exercises and resources to fully embed your new knowledge. This second edition includes a completely new chapter on machine learning in Go, guiding you from the foundation statistics techniques through simple regression and clustering to classification, neural networks, and anomaly detection. Other chapters are expanded to cover using Go with Docker and Kubernetes, Git, WebAssembly, JSON, and more. If you take the Go programming language seriously, the second edition of this book is an essential guide on expert techniques.
Table of Contents (20 chapters)
Title Page

Using standard output

Standard output is more or less equivalent to printing on the screen. However, using standard output might require the use of functions that do not belong to the fmt package, which is why it is presented in its own section.

The relevant technique will be illustrated in stdOUT.go and will be offered in three parts. The first part of the program is as follows:

package main 
import ( 

So, stdOUT.go will use the io package instead of the fmt package. The os package is used for reading the command-line arguments of the program and for accessing os.Stdout.

The second portion of stdOUT.go contains the following Go code:

func main() { 
    myString := "" 
    arguments := os.Args 
    if len(arguments) == 1 { 
        myString = "Please give me one argument!" 
    } else { 
        myString = arguments[1] 

The myString variable holds the text that will be printed on the screen, which is either the first command-line argument of the program or, if the program was executed without any command-line arguments, a hardcoded text message.

The third part of the program is as follows:

    io.WriteString(os.Stdout, myString) 
    io.WriteString(os.Stdout, "\n") 

In this case, the io.WriteString() function works in the same way as the fmt.Print() function; however, it takes only two parameters. The first parameter is the file you want to write to, which, in this case, is os.Stdout, and the second parameter is a string variable.

Strictly speaking, the type of the first parameter of the io.WriteString() function should be io.Writer, which requires a slice of bytes as the second parameter. However, in this case, a string variable does the job just fine. You will learn more about slices in Chapter 3, Working with Basic Go Data Types.

Executing stdOUT.go will produce the following output:

$ go run stdOUT.go
Please give me one argument!
$ go run stdOUT.go 123 12

The preceding output verifies that the io.WriteString() function sends the contents of its second parameter onto the screen when its first parameter is os.Stdout.