GO Tutorial: Getting started

Go 를 처음 접하는 개발자의 시점에서 Basic syntax를 정리해보려 한다.

Packages and Imports

• This code groups the imports into a parenthesized, factored import statement

• In Go, a name is exported if it begins with a capital letter

  package main
  
  import (
    "fmt"
    "math/rand"
  )
  
  func main() {
    fmt.Println("My favorite number is", rand.Intn(10))
  }
  

Functions

• A function can take zero or more arguments

• Each argument has a type beside or when more than one consecutive named function parameters share a type, omit the type from all but the declare at the end

  func swap(x, y string) (string, string) {
    return y, x
  }
  

  • Multiple results: a function can return any number of results

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

  • Naked return: a return statement without arguments returns the named return values
  • defer: excute something after finish the function

Basic Types

type	others	zero values	note
bool		false
string		””
int	int8 int16 int32 int64	0
unint	uint8 uint16 uint32 uint64 uintptr	0
byte			alias for uint8
rune			alias for int32
float32	float64	0
complex64	complex128

Variables and Constant

• The var statement declares a list of variables

  var version float64 = 16.3
  // OR
  vers := 16.3 // inference type: float64
  const language string = "Golang"
  

  • Short variable declarations(:=): short assignment statement can be used in place of a var declaration with implicit type inside a function. Short variable declarations does not support outside of a function
  • Constants can be character, string, boolean, or numeric values
  • Constants cannot be declared using the := syntax.

for, range, …args

• The init and post statements are optional

• At that point you can drop the semicolons: C’s while is spelled for in Go

  for i := 0; i < 10; i++ {
    sum += i
  }
  

  • If you omit the loop condition it loops forever, so an infinite loop is compactly expressed

  for index, number := range numbers {
    fmt.Println(index, number)
  }
  

  • For looping through an array, range can be used. first return value is index, and second return value is value in the array[index]

if Statement

• Like for, the if statement can start with a short statement to execute before the condition

• Variables declared inside an if short statement are also available inside any of the else blocks

  if v := math.Pow(x, n); v < lim {
  	return v
  } else {
  	fmt.Printf("%g >= %g\n", v, lim)
  }
  

Switch Statement

• Go’s switch is like the one in C, C++, Java, JavaScript, and PHP, except that Go only runs the selected case, not all the cases that follow.

  today := time.Now().Weekday()
  switch time.Saturday {
  case today + 0:
    fmt.Println("Today.")
  case today + 1:
    fmt.Println("Tomorrow.")
  case today + 2:
    fmt.Println("In two days.")
  default:
    fmt.Println("Too far away.")
  }
  

Defer

• A defer statement defers the execution of a function until the surrounding function returns.

• Deferred function calls are pushed onto a stack. When a function returns, its deferred calls are executed in last-in-first-out order.

  func main() {
    fmt.Println("counting")
  
    for i := 0; i < 10; i++ {
      defer fmt.Println(i)
    }
  
    fmt.Println("done")
  }
  

Reference

• A Tour of Go
• Go Introduction