GoLang Cheat Sheet by andanhm

package main

import "fmt"

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

$ cd $HOME/go/src/hello
$ go run main.go
Hello, World!!
$ go build
$ ./hello
Hello, World!!

bool

string

int  int8  int16  int32  int64
uint uint8 uint16 uint32 uint64 uintptr

byte // alias for uint8

rune // alias for int32 ~= a character (Unicode code point) 

float32 float64

complex64 complex128

const country = "india"

// declaration without initialization
var age int 
// declaration with initialization
var age int = 23 
// declare and init multiple at once
var age, pincode int = 23, 577002
// type omitted, will be inferred
var age = 23 

// simple function
func person() {
 // shorthand, only within func bodies
 // type is always implicit
 age := 23 
}

// Can have function with params
func person(firstName string, lastName string) {}

// Can have multiple params of the same type
func person(firstName, lastName string) {}

// Can return type declaration
func person() int {
    return 23
}

// Can return multiple values at once
func person() (int, string) {
    return 23, "vinay"
}
var age, name = person()

// Can return multiple named results
func person() (age int, name string) {
    age = 23
    name = "vinay"
    return
}
var age, name = person()

// Can return function
func person() func() (string,string)  {
     area:=func() (string,string) {
          return "street", "city"
      }
      return area
}

if age < 18 {
      return errors.New("not allowed to enter")
}

// Conditional statement
if err := Request("google.com"); err != nil {
    return err
}

// Type assertion inside
var age interface{}
age = 23
if val, ok := age.(int); ok {
    fmt.Println(val)
}

for i := 1; i < 3; i++ {
}
	// while loop syntax
	for i < 3 { 
	}
	// Can omit semicolons if there is only a condition
	for i < 10 { 
	}
	// while (true) like syntax
	for { 
	}

// switch statement
switch runtime.GOOS {
  case "darwin": {
	// cases break automatically
   }
   case "linux": {
   }
   default:
}

	// can have an assignment statement before the switch statement
	switch os := runtime.GOOS; os {
	case "darwin":
	default:
	}

	// comparisons in switch cases
	os := runtime.GOOS
	switch {
	case os == "darwin":
	default:
	}

	// cases can be presented in comma-separated lists
	switch os {
	case "darwin", "linux":
	}

var a [3]int // declare an int array with length 3. 
	var a = [3]int {1, 2, 3} // declare and initialize a slice
	a := [...]int{1, 2} // elipsis -> Compiler figures out array length
	a[0] = 1     // set elements
	i := a[0]     // read elements
	var b = a[lo:hi]	// creates a slice (view of the array) from index lo to hi-1
	var b = a[1:4]		// slice from index 1 to 3
	var b = a[:3]		// missing low index implies 0
	var b = a[3:]		// missing high index implies len(a)
	a =  append(a,17,3)	// append items to slice a
	c := append(a,b...)	// concatenate slices a and b
	
	// create a slice with make
	a = make([]int, 5, 5)	// first arg length, second capacity
	a = make([]int, 5)	// capacity is optional

// loop over an array/ slice / struct
for index, element := range a {
    
}

type Address struct {
  Street string
  City   string
}

type Employee struct {
  Name    string
  Age     int
  Address Address
}

// Can declare methods on structs.
func (emp Employee) Display() string {
  // accessing member
  name:=emp.Name
  return fmt.Sprintf("Name %s",name)
}
// Initialize the map with the type
// map key is city value employees working
bookmyshow := make(map[string][]Employee)

// Create new/updates the key value pair
bookmyshow["Pune"] = []Employee{}
bookmyshow["Bangalore"] = []Employee{
   Employee{
    Name: "Andan H M",
    Age:  23,
    Address: Address{
     Street: "KB Extension",
     City:   "Davanagere",
   },
 },
},

// Determains the the length of the map
_ = len(bookmyshow)

// read the item from the map
employees := bookmyshow["Bangalore"]

// loop over an array, slice, struct array
for index, element := range employees {
  // read the element from the struct
  fmt.Println(index, element.Display())
}

// Delete the key from the map
delete(bookmyshow, "Pune")

Interface type that specifies zero methods is known as the empty interface

var i interface{}
i = 42

// Reflection: type switch specify types
switch v := i.(type) {
 case int:
   fmt.Printf("(%v, %T)\n", i, i)
 case string:
  fmt.Printf("(%v, %T)\n", i, i)
 default:
  fmt.Printf("Unknow type %T!\n", v)
}

Interfaces are named collections of method signatures.

type error interface {
    Error() string
}

package main

import (
 "io"
 "net/http"
)

func health(w http.ResponseWriter, r *http.Request) {
  w.WriteHeader(http.StatusOK)
  io.WriteString(w, "Ok")
}

func main() {
 http.HandleFunc("/health", health)
 http.ListenAndServe(":8080", nil)
}

package main

import  "fmt"

func main() {
 n := 2
 
 // "make" the channel, which can be used
 // to move the int datatype
 out := make(chan int)

 // run this function as a goroutine
 // the channel that we made is also provided
 go Square(n, out)

 // Any output is received on this channel
 // print it to the console and proceed
 fmt.Println(<-out)
}

func Square(n int, out chan<- int) {
 result := n * n
 
 //pipes the result into it
 out <- result
}

package main

import (
 "encoding/json"
 "encoding/xml"
 "fmt"
)

type Employee struct {
 Name string `json:"name" xml:"name"`
 Age  int    `json:"age" xml:"age"`
}

func main() {
 emp := Employee{
  Name: "andan.h",
  Age:  27,
 }
 // Marshal:  refers to the process of converting 
 // the data or the objects into a byte-stream
 jsonData, _ := json.Marshal(emp)
 fmt.Println(string(jsonData))
 xmlData, _ := xml.Marshal(emp)
 fmt.Println(string(xmlData))

 // Unmarshal:  refers to the reverse process of
 // converting the byte-stream back to data or object
 json.Unmarshal(jsonData, &emp)
 fmt.Println(emp)
}