Go.md

Go

https://golang.org/

CLI tool

Run

go run myapp.go

Compile:

go build myapp.go

Code example

package main

import ("fmt")

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

Note: package main = compiles to executable file.

func HandleLambdaEvent(event MyEvent) (MyResponse, error) {
  return MyResponse{Message: fmt.Sprintf("%s is %d years old!", event.Name, event.Age)}, nil
}

Note: returns multiple values (MyResponse, error).

Packages

https://pkg.go.dev/std

import (
  "package1"
  p2 "package2"
)

Documentation

go doc fmt
go doc fmt.Println

Local packages

You define your module my_app in go.mod, then you can reference subfolders e.g. import "my_app/internal/pkg/db"

Linting and formatting

go vet main.go

go fmt main.go
gofmt -w main.go

The Go language

Variables

var firstName string
var age int8 // int8-64, uint8-64
var percentageWater float = 0.70
var isHuman bool = false

const earthsGravity = 9.80665

Structs/Collections/Interfaces

type Album struct {
    ID     string  `json:"id"`
    Title  string  `json:"title"`
    Artist string  `json:"artist"`
    Price  float64 `json:"price"`
}

// albums slice to seed record album data.
var albums = [] album {
    {ID: "1", Title: "Blue Train", Artist: "John Coltrane", Price: 56.99},
    {ID: "2", Title: "Jeru", Artist: "Gerry Mulligan", Price: 17.99},
    {ID: "3", Title: "Sarah Vaughan and Clifford Brown", Artist: "Sarah Vaughan", Price: 39.99},
}

type AlbumInterface interface {
    ID     string
    Title  string
    Artist string
    Price  float64
}

Private and public

privateFunction
PublicFunction

Short variable declarations with :=

myVariable := aFunction()

Underscore _ assignment

stringBody, _ := json.Marshal(body)

This just ignores the second value.

Tags (e.g. JSON field names)

Tags: https://medium.com/golangspec/tags-in-golang-3e5db0b8ef3e

user.Tag.Lookup("json")

Environment variables

os.Getenv("FOO")
os.Setenv("FOO", "1")
os.Environ()

Command-line arguments: flags

https://gobyexample.com/command-line-flags

JSON

Unmarshal = Parse

body := BodyParameters{}
json.Unmarshal([]byte(req.Body), &body)

Marshal = Format as string

data, error := json.Marshal(pigeon)
fmt.Println(string(data))

HTTP server

package main

import (
	"fmt"
	"net/http"
)

func main() {
    http.HandleFunc("/hello-world", func(w http.ResponseWriter, r *http.Request){
        fmt.Fprintf(w, "Hello world") // or: fmt.Fprint(w, myFunction())
    })
    http.ListenAndServe(":80", nil)
}

Building a RESTful API

https://golang.org/doc/tutorial/web-service-gin

Go on AWS Lambda with Docker

https://github.com/Binogi/golang-aws-lambda-docker