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2021-02-21T23:40:59Z

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Shameless rip from https://devhints.io/go
```
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 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)
}

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 amount 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()

}

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 current value of d, unless we use a pointer to get final value at end of 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())
}
```

Golang Cheatsheet - Revision history

Busk: Created page with "Shameless rip from https://devhints.io/go ``` Introduction A tour of Go (tour.golang.org) Go repl (repl.it) Golang wiki (github.com) Hello world hello.go package main import..."