Go – Vipin V

Getting Started

hello.go

package main
 
import "fmt"
 
func main() {
    fmt.Println("Hello, world!")
}

Run directly

$ go run hello.go
Hello, world!

Or try it out in the Go repl (opens in a new tab)

Variables

var s1 string
s1 = "Learn Go!"
 
// declare multiple variables at once
var b, c int = 1, 2
var d = true

Short declaration

s1 := "Learn Go!"        // string
b, c := 1, 2             // int
d := true                // bool

See: Basic types

Functions

package main
 
import "fmt"
 
// The entry point of the programs
func main() {
    fmt.Println("Hello world!")
    say("Hello Go!")
}
 
func say(message string) {
    fmt.Println("You said: ", message)
}

See: Functions

Comments

// Single line comment
 
/* Multi-
 line comment */

If statement

if true {
    fmt.Println("Yes!")
}

See: Flow control

Go Basic types

Strings

s1 := "Hello" + "World"
 
s2 := `A "raw" string literal
can include line breaks.`
 
// Outputs: 10
fmt.Println(len(s1))
 
// Outputs: Hello
fmt.Println(string(s1[0:5]))

Strings are of type string.

Numbers

num := 3         // int
num := 3.        // float64
num := 3 + 4i    // complex128
num := byte('a') // byte (alias: uint8)
 
var u uint = 7        // uint (unsigned)
var p float32 = 22.7  // 32-bit float

Operators

x := 5
x++
fmt.Println("x + 4 =", x + 4)
fmt.Println("x * 4 =", x * 4)

See: More Operators

Booleans

isTrue   := true
isFalse  := false

Operators

fmt.Println(true && true)   // true 
fmt.Println(true && false)  // false
fmt.Println(true || true)   // true
fmt.Println(true || false)  // true
fmt.Println(!true)          // false

See: More Operators

Arrays {.row-span-2}

┌────┬────┬────┬────┬─────┬─────┐
| 2  | 3  | 5  | 7  | 11  | 13  |
└────┴────┴────┴────┴─────┴─────┘
  0    1    2    3     4     5

primes := [...]int{2, 3, 5, 7, 11, 13}
fmt.Println(len(primes)) // => 6
 
// Outputs: [2 3 5 7 11 13]
fmt.Println(primes)
 
// Same as [:3], Outputs: [2 3 5]
fmt.Println(primes[0:3])

var a [2]string
a[0] = "Hello"
a[1] = "World"
 
fmt.Println(a[0], a[1]) //=> Hello World
fmt.Println(a)   // => [Hello World]

2d array

var twoDimension [2][3]int
for i := 0; i < 2; i++ {
    for j := 0; j < 3; j++ {
        twoDimension[i][j] = i + j
    }
}
// => 2d:  [[0 1 2] [1 2 3]]
fmt.Println("2d: ", twoDimension)

Pointers

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

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

a := new(int)
*a = 234

See: Pointers (opens in a new tab)

Slices

s := make([]string, 3)
s[0] = "a"
s[1] = "b"
s = append(s, "d")
s = append(s, "e", "f")
 
fmt.Println(s)
fmt.Println(s[1])
fmt.Println(len(s))
fmt.Println(s[1:3])
 
slice := []int{2, 3, 4}

Constants

const s string = "constant"
const Phi = 1.618
const n = 500000000
const d = 3e20 / n
fmt.Println(d)

Type conversions

i := 90
f := float64(i)
u := uint(i)
 
// Will be equal to the character Z
s := string(i)

How to get int string?

i := 90
 
// need import "strconv"
s := strconv.Itoa(i)
fmt.Println(s) // Outputs: 90

Go Strings

Strings function

package main
 
import (
	"fmt"
	s "strings"
)
 
func main() {
    /* Need to import strings as s */
	fmt.Println(s.Contains("test", "e"))
 
    /* Build in */
    fmt.Println(len("hello"))  // => 5
    // Outputs: 101
	fmt.Println("hello"[1])
    // Outputs: e
	fmt.Println(string("hello"[1]))
 
}

fmt.Printf {.row-span-2 .col-span-2}

package main
 
import (
	"fmt"
	"os"
)
 
type point struct {
	x, y int
}
 
func main() {
	p := point{1, 2}
	fmt.Printf("%v\n", p)                        // => {1 2}
	fmt.Printf("%+v\n", p)                       // => {x:1 y:2}
	fmt.Printf("%#v\n", p)                       // => main.point{x:1, y:2}
	fmt.Printf("%T\n", p)                        // => main.point
	fmt.Printf("%t\n", true)                     // => TRUE
	fmt.Printf("%d\n", 123)                      // => 123
	fmt.Printf("%b\n", 14)                       // => 1110
	fmt.Printf("%c\n", 33)                       // => !
	fmt.Printf("%x\n", 456)                      // => 1c8
	fmt.Printf("%f\n", 78.9)                     // => 78.9
	fmt.Printf("%e\n", 123400000.0)              // => 1.23E+08
	fmt.Printf("%E\n", 123400000.0)              // => 1.23E+08
	fmt.Printf("%s\n", "\"string\"")             // => "string"
	fmt.Printf("%q\n", "\"string\"")             // => "\"string\""
	fmt.Printf("%x\n", "hex this")               // => 6.86578E+15
	fmt.Printf("%p\n", &p)                       // => 0xc00002c040
	fmt.Printf("|%6d|%6d|\n", 12, 345)           // => |    12|   345|
	fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)     // => |  1.20|  3.45|
	fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)   // => |1.20  |3.45  |
	fmt.Printf("|%6s|%6s|\n", "foo", "b")        // => |   foo|     b|
	fmt.Printf("|%-6s|%-6s|\n", "foo", "b")      // => |foo   |b     |
 
	s := fmt.Sprintf("a %s", "string")
	fmt.Println(s)
 
	fmt.Fprintf(os.Stderr, "an %s\n", "error")
}

Function examples

Example	Result
Contains("test", "es")	true
Count("test", "t")	2
HasPrefix("test", "te")	true
HasSuffix("test", "st")	true
Index("test", "e")	1
Join([]string{"a", "b"}, "-")	a-b
Repeat("a", 5)	aaaaa
Replace("foo", "o", "0", -1)	f00
Replace("foo", "o", "0", 1)	f0o
Split("a-b-c-d-e", "-")	[a b c d e]
ToLower("TEST")	test
ToUpper("test")	TEST

Go Flow control

Conditional

 
a := 10
 
if a > 20 {
    fmt.Println(">")
} else if a < 20 {
    fmt.Println("<")
} else {
    fmt.Println("=")
}

Statements in if

x := "hello go!"
 
if count := len(x); count > 0 {
    fmt.Println("Yes")
}

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

Switch

x := 42.0
switch x {
case 0:
case 1, 2:
    fmt.Println("Multiple matches")
case 42:   // Don't "fall through".
    fmt.Println("reached")
case 43:
    fmt.Println("Unreached")
default:
    fmt.Println("Optional")
}

See: Switch (opens in a new tab)

For loop

for i := 0; i <= 10; i++ {
  fmt.Println("i: ", i)
}

For-Range loop

nums := []int{2, 3, 4}
sum := 0
for _, num := range nums {
    sum += num
}
fmt.Println("sum:", sum)

While loop

i := 1
for i <= 3 {
    fmt.Println(i)
    i++
}

Continue keyword

for i := 0; i <= 5; i++ {
    if i % 2 == 0 {
        continue
    }
    fmt.Println(i)
}

Break keyword

for {
    fmt.Println("loop")
    break
}

Go Structs & Maps

Defining {.row-span-2}

package main
 
import (
	"fmt"
)
 
type Vertex struct {
	X int
	Y int
}
 
func main() {
	v := Vertex{1, 2}
	v.X = 4
	fmt.Println(v.X, v.Y) // => 4 2
}

See: Structs (opens in a new tab)

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.

Maps {.row-span-2}

m := make(map[string]int)
m["k1"] = 7
m["k2"] = 13
fmt.Println(m) // => map[k1:7 k2:13]
 
v1 := m["k1"]
fmt.Println(v1)     // => 7
fmt.Println(len(m)) // => 2
 
delete(m, "k2")
fmt.Println(m) // => map[k1:7]
 
_, prs := m["k2"]
fmt.Println(prs) // => false
 
n := map[string]int{"foo": 1, "bar": 2}
fmt.Println(n) // => map[bar:2 foo:1]

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.

Go Functions

Multiple arguments

func plus(a int, b int) int {
    return a + b
}
func plusPlus(a, b, c int) int {
    return a + b + c
}
fmt.Println(plus(1, 2))
fmt.Println(plusPlus(1, 2, 3))

Multiple return

func vals() (int, int) {
    return 3, 7
}
 
a, b := vals()
fmt.Println(a)    // => 3
fmt.Println(b)    // => 7

Function literals

r1, r2 := func() (string, string) {
    x := []string{"hello", "cheatsheets.zip"}
    return x[0], x[1]
}()
 
// => hello cheatsheets.zip
fmt.Println(r1, r2)

Naked returns

func split(sum int) (x, y int) {
  x = sum * 4 / 9
  y = sum - x
  return
}
 
x, y := split(17)
fmt.Println(x)   // => 7
fmt.Println(y)   // => 10

Note that using naked returns hurts readability.

Variadic functions

func sum(nums ...int) {
    fmt.Print(nums, " ")
    total := 0
    for _, num := range nums {
        total += num
    }
    fmt.Println(total)
}
sum(1, 2)     //=> [1 2] 3
sum(1, 2, 3)  // => [1 2 3] 6
 
nums := []int{1, 2, 3, 4}
sum(nums...)  // => [1 2 3 4] 10

init function

import --> const --> var --> init()

var num = setNumber()
 
func setNumber() int {
    return 42
}
func init() {
    num = 0
}
func main() {
    fmt.Println(num) // => 0
}

Functions as values

func main() {
    // assign a function to a name
    add := func(a, b int) int {
        return a + b
    }
    // use the name to call the function
    fmt.Println(add(3, 4)) // => 7
}

Closures 1

func scope() func() int{
    outer_var := 2
    foo := func() int {return outer_var}
    return foo
}
 
// Outpus: 2
fmt.Println(scope()())

Closures 2

func outer() (func() int, int) {
    outer_var := 2
    inner := func() int {
        outer_var += 99
        return outer_var
    }
    inner()
    return inner, outer_var
}
inner, val := outer()
fmt.Println(inner()) // => 200
fmt.Println(val)     // => 101

Go Packages

Importing {.row-span-2}

import "fmt"
import "math/rand"

Same as

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

See: Importing (opens in a new tab)

Aliases {.row-span-2}

import r "math/rand"

import (
    "fmt"
    r "math/rand"
)

r.Intn()

Packages

package main
 
// An internal package may be imported only by another package
// that is inside the tree rooted at the parent of the internal directory
package internal

See: Internal packages (opens in a new tab)

Exporting names

// Begin with a capital letter
func Hello () {
  ···
}

See: Exported names (opens in a new tab)

Go Concurrency

Goroutines {.row-span-2}

package main
 
import (
	"fmt"
	"time"
)
 
func f(from string) {
	for i := 0; i < 3; i++ {
		fmt.Println(from, ":", i)
	}
}
 
func main() {
	f("direct")
	go f("goroutine")
 
	go func(msg string) {
		fmt.Println(msg)
	}("going")
 
	time.Sleep(time.Second)
	fmt.Println("done")
}

See: Goroutines (opens in a new tab), Channels (opens in a new tab)

WaitGroup {.row-span-2}

package main
 
import (
	"fmt"
	"sync"
	"time"
)
 
func w(id int, wg *sync.WaitGroup) {
	defer wg.Done()
	fmt.Printf("%d starting\n", id)
 
	time.Sleep(time.Second)
	fmt.Printf("%d done\n", id)
}
 
func main() {
	var wg sync.WaitGroup
	for i := 1; i <= 5; i++ {
		wg.Add(1)
		go w(i, &wg)
	}
	wg.Wait()
}

See: WaitGroup (opens in a new tab)

Closing channels

ch <- 1
ch <- 2
ch <- 3
close(ch) // Closes a channel

// Iterate the channel until closed
for i := range ch {
  ···
}

// Closed if `ok == false`
v, ok := <- ch

See: Range and close (opens in a new tab)

Buffered channels

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

See: Buffered channels (opens in a new tab)

Go Error control

Deferring functions

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

Lambda defer

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 current value of d, unless we use a pointer to get final value at end of main.

Defer

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

See: Defer, panic and recover (opens in a new tab)

Go Methods {.cols-2}

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()

See: Methods (opens in a new tab)

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

See: Pointer receivers (opens in a new tab)

Go Interfaces {.cols-2}

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())
}

Miscellaneous

Keywords

break
default
func
interface
select
case
defer
go
map
struct
chan
else
goto
package
switch
const
fallthrough
if
range
type
continue
for
import
return
var {.cols-3 .marker-none}

Operators and punctuation


+	&	+=	&=	&&	==	!=	(	)
-	\|	-=	\|=	\|\|	<	<=	[	]
*	^	*=	^=	<-	>	>=	{	}
/	<<	/=	<<=	++	=	:=	,	;
%	>>	%=	>>=	--	!	...	.	:
	&^	&^=

Also see {.cols-1}

Devhints (opens in a new tab) (devhints.io)
A tour of Go (opens in a new tab) (tour.go.dev)
Go wiki (opens in a new tab) (github.com)
Effective Go (opens in a new tab) (go.dev)
Go by Example (opens in a new tab) (gobyexample.com)
Awesome Go (opens in a new tab) (awesome-go.com)
JustForFunc Youtube (opens in a new tab) (youtube.com)
Style Guide (opens in a new tab) (github.com)

Sass Emacs


+	&	+=	&=	&&	==	!=	(	)
-	\|	-=	\|=	\|\|	<	<=	[	]
*	^	*=	^=	<-	>	>=	{	}
/	<<	/=	<<=	++	=	:=	,	;
%	>>	%=	>>=	--	!	...	.	:
	&^	&^=


+	&	+=	&=	&&	==	!=	(	)
-	\|	-=	\|=	\|\|	<	<=	[	]
*	^	*=	^=	<-	>	>=	{	}
/	<<	/=	<<=	++	=	:=	,	;
%	>>	%=	>>=	--	!	...	.	:
	&^	&^=


+	&	+=	&=	&&	==	!=	(	)
-	\|	-=	\|=	\|\|	<	<=	[	]
*	^	*=	^=	<-	>	>=	{	}
/	<<	/=	<<=	++	=	:=	,	;
%	>>	%=	>>=	--	!	...	.	:
	&^	&^=