01_Go_basics.md

Getting Started With Go

Let's study Go

A huge thank you to Calvin!

What is Go Language?

• Programming language developed by Google
• Syntax is similar to C language, but designed to handle Concurrency programming easily
  • Concurrency programming
    • Means that the program can do other things first while performing relatively time-consuming operations such as DB requests or network communication like web services
• Although it's a relatively recently emerged programming language, it's not complex and a practical language
• Representative projects that utilize Go include Docker and Kubernetes

Why Go?

• Go aims for a simple, concise, and intuitive language

  • Supports OOP
    • No concepts of class, objects, inheritance
  • Keywords used in Go are only 25, half the level of Java
    • Simple!
  • Although it's a compiled language, the compiler speed is very fast, so it can be used like an interpreter language

• Has a good build system

  • Build speed is very fast
    • Projects consisting of thousands of lines of code compile in just a few seconds!
  • Code import is based on off url import
    • So it's good for managing dependencies!
      • Go module allows you to hash URLs when importing
        • Similar to importing .lock files in other build systems!

Install Go on Ubuntu/Mac

1. Install Go 1.14

Ubuntu

• Install using longsleep/golang-backports PPA

  sudo add-apt-repository ppa:longsleep/golang-backports
  sudo apt update
  sudo apt install golang-go

MacOS

• Download & install package from golang.org

2. Check Go version

Ubuntu

chloe@chloe-XPS-15-9570 ~
$ go version
go version go1.14.2 linux/amd64

MacOS

~ via ⬢ v14.15.1
➜ go version
go version go1.15.6 darwin/amd64

3. Workspace setup

• Create a directory to proceed with Go projects
  • ex) /Users/chloe/workspace/go
• Create 3 directories inside that directory as follows
  • bin
    • Where OS-specific executable binary files are stored after source code is compiled
  • pkg
    • Where library files are stored after packages needed for the project are compiled
  • src
    • Where written source code and open source codes are stored

4. Environment variable setup

• Go has 2 environment variables - GOPATH & GOROOT
• GOROOT
  • Where Go binaries are located
  • If you install with sudo apt install golang-go, Go is installed in the default path, so no need to modify separately!
    • On Mac, it's installed in /usr/local/go
• GOPATH
  • User go environment path
  • Need to set where project files are located
  • When importing packages with go import, it's loaded from GOPATH
  • Generally set GOPATH to $HOME/go
    • Important because when doing go install or go import, go looks for GOPATH!

4-1. Ubuntu $GOPATH setup

GOPATH setup

export GOPATH=$HOME/go

PATH setup

export PATH=$PATH:$GOPATH/bin

4-2. MacOS $GOPATH setup

Add the following to ~/.zshrc

export GOPATH="/Users/chloe/workspace/go"
export PATH="$GOPATH:$PATH"

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After setting $GOPATH, you can use the go env command to check if it's properly applied!

5. src in $GOPATH

• Go downloads and stores downloaded codes in $GOPATH/src classified by downloaded domain
  • ex) github.com, golang.org, google-golang.org, etc.
  • For source code I write, I'll create a directory with github user name inside github.com

Getting started with Go

1. Main package

• Naming the package main.go means you will compile this project and use it

  • That is, all packages except main.go are not compiled!

• Since main is the entry point, the compiler looks for packages named main first

  • ex) package main

• Go looks for a function called func main() {}

  • This is the entrypoint of the Go program!

• Automatically, the compiler first finds and executes the main package and the main function inside it

  • ex)

    main.go

    package main
    
    import "fmt"
    
    func main() {
     fmt.Println("Hello World")
    }

2. Packages and imports

• To export a function in Go, write it in upper-case

  • ex)

    something.go

    package something
    
    import "fmt"
    
    func saySeeya() {
     fmt.Println("See ya!")
    }
    
    func SayHello() {
     fmt.Println("Hello!")
    }

    main.go

    package main
    
    import (
     "fmt"
    
     "github.com/chloe-codes1/go101/something"
    )
    
    func main() {
     fmt.Println("Hello World")
     something.SayHello()
    }

Console output functions - println, print

Let's output

ex)

package main
import "fmt"

func main() {
 fmt.Print("Hello goorm!")
}

• print / println can be used without importing fmt package

• println and print differ in the presence of line break

  • To make a line break with print, use \n!

• Single quotes don't work!

  • Use double quotes

• print functions can output the results of operations inside functions!

  ex)

  package main
  
  func main() {
    var num1 int = 1000
    var num2 int = 1413
  
    println("Let's do addition ~ ", num1 + num2)
  }

  chloe@chloe-XPS-15-9570 ~/Workspace/Go/Go101
  $ ./calc
  Let's do addition ~  2413

fmt package

• Package for input/output
• How to use
  • Write import "fmt" below package main

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Useful Go resources recommended by Calvini

• gobyexample.com
• tour.golang.org
• blog.golang.org
• dave.cheney.net
• https://golang.org/doc/effective_go.html
  • must read!