Learning Go Programming Language

• Install Go on macOS
• Tutorial: Create a Go module – golang.org
• How to Write Go Code – golang.org
• Go Data Structures
• Arrays, slices (and strings): The mechanics of ‘append’
• Strings, bytes, runes and characters in Go
• Effective Go

Notes

package greetings

import "fmt"

// Hello returns a greeting for the named person.
func Hello(name string) string {
    // Return a greeting that embeds the name in a message.
    message := fmt.Sprintf("Hi, %v. Welcome!", name)
    return message
}

• In Go, a function whose name starts with a capital letter can be called by a function not in the same package. This is known in Go as an exported name.

• In Go, the := operator is a shortcut for declaring and initializing a variable in one line (Go uses the value on the right to determine the variable’s type). Taking the long way, you might have written this as:

var message string
message = fmt.Sprintf("Hi, %v. Welcome!", name)

• In Go, code executed as an application must go in a main package.

package greetings

import (
    "errors"
    "fmt"
)

func Hello(name string) (string, error) {
    if name == "" {
        return "", errors.New("empty name")
    }
    message := fmt.Sprintf("Hi, %v. Welcome!", name)
    return message, nil
}

• Returns two values: a string and an error. Your caller will check the second value to see if an error occurred. (Any Go function can return multiple values.)
• Import the Go standard library errors package so you can use its errors.New function.
  • The errors.New function returns an error with your message inside.
• Add nil (meaning no error) as a second value in the successful return. That way, the caller can see that the function succeeded.

package main

import (
    "fmt"
    "log"
    "ninegene.com/greetings"
)

func main() {
    log.SetPrefix("greetings: ")
    log.SetFlags(0)

    message, err := greetings.Hello("")

    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(message)
}

• Configure the log package to print the command name (“greetings: “) at the start of its log messages, without a time stamp or source file information.

$ go run hello.go
greetings: empty name
exit status 1

• That’s essentially how error handling in Go works: Return an error as a value so the caller can check for it.