golang_tutorial.go

package main

import (
  "fmt"
  "math"
  "runtime"
)

const Pi = 3.1415

func add(x int, y int) int {
  return x + y
}

func multiple_returns(x int) (d, t int) {
  d = x * 2
  t = x * 3
  return
}

func variable_declaration() {
  var a int
  var b string
  fmt.Println(a, b)
  var c, d int = 3, 4
  fmt.Println(c, d)
  /* implicit var, only inside a function */
  f := 123
  fmt.Println(f)
  /* some types */
  var ui8 uint8 = 255; /* byte */
  var xx uintptr = 18446744073709551615
  var fff float64 = 3.14159893274928376
  fmt.Println(ui8)
  fmt.Println(xx)
  fmt.Println(fff)
  /* type inference */
  var s1 string = "ok"
  s2 := s1
  s1 = "hey"
  fmt.Printf("%s, %s\n", s1, s2)
}

func loops() {
  sum := 0
  for i := 0; i < 10; i++ {
    sum += i
  }
  fmt.Println(sum)

  /* while */
  for sum < 100 {
    sum+=sum
  }
  fmt.Println(sum)

  /* infloop */
  sq := float64(sum)
  for {
    sq = math.Sqrt(sq)
    if sq < 10 {
      break
    }
  }
  fmt.Println(sq)
}

func not_a_number() {
  fmt.Println(math.Sqrt(-4)) /* NaN */
}

func if_short_statement() {
  /* if short statement */
  xxx := 2
  if yyy := xxx; yyy < 3 {
    fmt.Println("ok!")
  }
  // fmt.Println(yyy) // no yyy declared
}

func which_os() {
  fmt.Print("Go runs on ")
  switch os := runtime.GOOS; os {
  case "darwin":
    fmt.Println("OS X.")
  case "linux":
    fmt.Println("Linux.")
  default:
    // freebsd, openbsd,
    // plan9, windows...
    fmt.Printf("%s.", os)
  }
}

func pointers() {
  i := 42
  p := &i
  fmt.Println(*p)
  *p = 12345
  fmt.Println(i)
}

type Vec2 struct {
  x int
  y int
}

func vec_struct_and_pointer() {
  vv := Vec2{2, 3}
  fmt.Println(vv)
  fmt.Printf("x=%d, y=%d\n", vv.x, vv.y)
  p := &vv
  p.x = 7
  p.y = 9
  fmt.Printf("x=%d, y=%d\n", vv.x, vv.y)
}

func arrays() {
  var a [2]string
  a[0] = "hello"
  a[1] = "world"
  fmt.Println(a)

  b := []int{2, 3, 4, 5}
  for i := 0; i < len(b); i++ {
    fmt.Printf("- %d\n", b[i])
  }

  m := [][]int {
    []int{1, 2, 3},
    []int{4, 5, 6},
    []int{7, 8, 9},
  }
  for i := 0; i < len(m); i++ {
    for j := 0; j < len(m[i]); j++ {
      fmt.Printf("[%d]", m[i][j])
    }
    fmt.Printf("\n")
  }

  xx := []int{2, 3, 4, 5, 6, 7, 8}
  ss := xx[3:]
  fmt.Println(ss)
  ss = append(ss, 2, 3, 4)
  fmt.Println(ss)

  for i, v := range ss {
    fmt.Printf("%d -> %d\n", i, v)
  }
  for _, v := range ss { // skip index
    fmt.Println(v)
  }
}

func maps() {
  var players map[string]Vec2
  players = make(map[string]Vec2)
  players["player1"] = Vec2{4, 7}
  players["player2"] = Vec2{6, 1}

  for k, v := range players {
    fmt.Printf("%s => [%d, %d]\n", k, v.x, v.y)
  }
  
  m := make(map[string]int)
  m["a"] = 1
  m["b"] = 2
  m["c"] = 3
  delete(m, "b")

  for _, v := range m {
    fmt.Println(v)
  }
  
  elem, ok := m["c"]
  if ok {
    fmt.Println(elem)
  }
  
  elem, ok = m["b"]
  if !ok {
    fmt.Println("b is not set")
  }
}

func (vec2 *Vec2) Print() {
  fmt.Printf("VEC2: x=%d, y=%d\n", vec2.x, vec2.y)
}

func (vec2 *Vec2) Sprint() string {
  return fmt.Sprintf("VEC2: x=%d, y=%d\n", vec2.x, vec2.y)
}

func methods() {
  v1 := Vec2{2, 3}
  v1.Print()
  str := v1.Sprint()
  fmt.Println(str)
}

func main() {
  fmt.Printf("hello, vlsm, %d\n", add(2, 3))
  fmt.Println(multiple_returns(5))
  variable_declaration()
  loops()
  not_a_number()
  if_short_statement()
  which_os()
  pointers()
  vec_struct_and_pointer()
  arrays()
  maps()
  methods()
}