The Ultimate Go Cheatsheet 🚀 - Best Go Concepts 🔥

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Getting started

Introduction

A tour of Go (tour.golang.org)
Go repl (repl.it)
Golang wiki (github.com)

Hello world

hello.go

package main

import "fmt"

func main() {
  message := greetMe("world")
  fmt.Println(message)
}

func greetMe(name string) string {
  return "Hello, " + name + "!"
}

$ go build

Or try it out in the Go repl, or A Tour of Go.

Variables

Variable declaration

var msg string
msg = "Hello"

Shortcut of above (Infers type)

msg := "Hello"

Constants

const Phi = 1.618

Constants can be a character, string, boolean, or numeric values.

See: Constants

Basic types

Strings

str := "Hello"

str := `Multiline
string`

Strings are of type string.

Numbers

Typical types

num := 3          // int
num := 3.         // float64
num := 3 + 4i     // complex128
num := byte('a')  // byte (alias for uint8)

Other types

var u uint = 7        // uint (unsigned)
var p float32 = 22.7  // 32-bit float

Arrays

// var numbers [5]int
numbers := [...]int{0, 0, 0, 0, 0}

Arrays have a fixed size.

Slices

slice := []int{2, 3, 4}

slice := []byte("Hello")

Slices have a dynamic size, unlike arrays.

Pointers

func main () {
  b := *getPointer()
  fmt.Println("Value is", b)
}

{: data-line="2"}

func getPointer () (myPointer *int) {
  a := 234
  return &a
}

a := new(int)
*a = 234

Pointers point to a memory location of a variable. Go is fully garbage-collected.

See: Pointers

Type conversions

i := 2
f := float64(i)
u := uint(i)

See: Type conversions

Flow control

Conditional

if day == "sunday" || day == "saturday" {
  rest()
} else if day == "monday" && isTired() {
  groan()
} else {
  work()
}

See: If

Statements in if

if _, err := doThing(); err != nil {
  fmt.Println("Uh oh")
}

A condition in an if statement can be preceded with a statement before a ;. Variables declared by the statement are only in scope until the end of the if.

See: If with a short statement

Switch

switch day {
  case "sunday":
    // cases don't "fall through" by default!
    fallthrough

  case "saturday":
    rest()

  default:
    work()
}

See: Switch

For loop

for count := 0; count <= 10; count++ {
  fmt.Println("My counter is at", count)
}

See: For loops

For-Range loop

entry := []string{"Jack","John","Jones"}
for i, val := range entry {
  fmt.Printf("At position %d, the character %s is present\n", i, val)
}

See: For-Range loops

While loop

n := 0
x := 42
for n != x {
  n := guess()
}

See: Go's "while"

Functions

Lambdas

myfunc := func() bool {
  return x > 10000
}

Functions are first-class objects.

Multiple return types

a, b := getMessage()

func getMessage() (a string, b string) {
  return "Hello", "World"
}

Named return values

func split(sum int) (x, y int) {
  x = sum * 4 / 9
  y = sum - x
  return
}

By defining the return value names in the signature, a return (no args) will return variables with those names.

See: Named return values

Packages

Importing

import "fmt"
import "math/rand"

import (
  "fmt"        // gives fmt.Println
  "math/rand"  // gives rand.Intn
)

Both are the same.

See: Importing

Aliases

import r "math/rand"

r.Intn()

Exporting names

func Hello () {
  ···
}

Exported names begin with capital letters.

See: Exported names

Packages

package hello

Every package file has to start with package.

Concurrency

Goroutines

func main() {
  // A "channel"
  ch := make(chan string)

  // Start concurrent routines
  go push("Moe", ch)
  go push("Larry", ch)
  go push("Curly", ch)

  // Read 3 results
  // (Since our goroutines are concurrent,
  // the order isn't guaranteed!)
  fmt.Println(<-ch, <-ch, <-ch)
}

func push(name string, ch chan string) {
  msg := "Hey, " + name
  ch <- msg
}

Channels are concurrency-safe communication objects, used in goroutines.

See: Goroutines, Channels

Buffered channels

ch := make(chan int, 2)
ch <- 1
ch <- 2
ch <- 3
// fatal error:
// all goroutines are asleep - deadlock!

Buffered channels limit the number of messages it can keep.

See: Buffered channels

Closing channels

Closes a channel

ch <- 1
ch <- 2
ch <- 3
close(ch)

Iterates across a channel until its closed

for i := range ch {
  ···
}

Closed if `ok == false`

v, ok := <- ch

See: Range and close

WaitGroup

import "sync"

func main() {
  var wg sync.WaitGroup

  for _, item := range itemList {
    // Increment WaitGroup Counter
    wg.Add(1)
    go doOperation(item)
  }
  // Wait for goroutines to finish
  wg.Wait()

}

{: data-line="1,4,8,12"}

func doOperation(item string) {
  defer wg.Done()
  // do operation on item
  // ...
}

A WaitGroup waits for a collection of goroutines to finish. The main goroutine calls Add to set the number of goroutines to wait for. The goroutine calls wg.Done() when it finishes.
See: WaitGroup

Error control

Defer

func main() {
  defer fmt.Println("Done")
  fmt.Println("Working...")
}

Defers running a function until the surrounding function returns.
The arguments are evaluated immediately, but the function call is not ran until later.

See: Defer, panic and recover

Deferring functions

func main() {
  defer func() {
    fmt.Println("Done")
  }()
  fmt.Println("Working...")
}

Lambdas are better suited for defer blocks.

func main() {
  var d = int64(0)
  defer func(d *int64) {
    fmt.Printf("& %v Unix Sec\n", *d)
  }(&d)
  fmt.Print("Done ")
  d = time.Now().Unix()
}

The defer func uses the current value of d, unless we use a pointer to get the final value at end of the main.

Structs

Defining

type Vertex struct {
  X int
  Y int
}

func main() {
  v := Vertex{1, 2}
  v.X = 4
  fmt.Println(v.X, v.Y)
}

See: Structs

Literals

v := Vertex{X: 1, Y: 2}

// Field names can be omitted
v := Vertex{1, 2}

// Y is implicit
v := Vertex{X: 1}

You can also put field names.

Pointers to structs

v := &Vertex{1, 2}
v.X = 2

Doing v.X is the same as doing (*v).X, when v is a pointer.

Methods

Receivers

type Vertex struct {
  X, Y float64
}

func (v Vertex) Abs() float64 {
  return math.Sqrt(v.X * v.X + v.Y * v.Y)
}

v := Vertex{1, 2}
v.Abs()

There are no classes, but you can define functions with receivers.

See: Methods

Mutation

func (v *Vertex) Scale(f float64) {
  v.X = v.X * f
  v.Y = v.Y * f
}

v := Vertex{6, 12}
v.Scale(0.5)
// `v` is updated

By defining your receiver as a pointer (*Vertex), you can do mutations.

See: Pointer receivers

Interfaces

A basic interface

type Shape interface {
  Area() float64
  Perimeter() float64
}

Struct

type Rectangle struct {
  Length, Width float64
}

Struct Rectangle implicitly implements interface Shape by implementing all of its methods.

Methods

func (r Rectangle) Area() float64 {
  return r.Length * r.Width
}

func (r Rectangle) Perimeter() float64 {
  return 2 * (r.Length + r.Width)
}

The methods defined in Shape are implemented in Rectangle.

Interface example

func main() {
  var r Shape = Rectangle{Length: 3, Width: 4}
  fmt.Printf("Type of r: %T, Area: %v, Perimeter: %v.", r, r.Area(), r.Perimeter())
}

References

Official resources

A tour of Go (tour.golang.org)
Golang wiki (github.com)
Effective Go (golang.org)

The Ultimate Go Cheatsheet 🚀 - Best Go Concepts 🔥

Garvit Motwani

Getting started

Introduction

Hello world

hello.go

Variables

Variable declaration

Shortcut of above (Infers type)

Constants

Basic types

Strings

Numbers

Typical types

Other types

Arrays

Slices

Pointers

Type conversions

Flow control

Conditional

Statements in if

Switch

For loop

For-Range loop

While loop

Functions

Lambdas

Multiple return types

Named return values

Packages

Importing

Aliases

Exporting names

Packages

Concurrency

Goroutines

Buffered channels

Closing channels

Closes a channel

Iterates across a channel until its closed

Closed if ok == false

WaitGroup

Error control

Defer

Deferring functions

Structs

Defining

Literals

Pointers to structs

Methods

Receivers

Mutation

Interfaces

A basic interface

Struct

Methods

Interface example

References

Official resources

Other links

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Related

Closed if `ok == false`