Go Things

Compilation

to generate object file go :

$ go tool compile main.go

to generate assmebly :

$ go tool compile -S main.go

Named return

package main

import "fmt"

func add(x, y int) (p int) {
    p = x + y
    // Notice you dont have to use := to initialise p
    // because it's already declared in the return
    return
}

func main() {
    fmt.Println(add(3, 4))
}

Data Types

byte : alias for uint8 rune : alias for int32

uint     unsigned, either 32 or 64 bits
int      signed, either 32 or 64 bits
uintptr  unsigned integer large enough to store the uninterpreted bits of a pointer value

If Short Hand

func funcPow( x,n,limit float64 ) float64 {
    if v:= math.Pow(x,n);
    v < limit {
        return v
    }
    return limit
}

Defer

package main

import "fmt"

func main() {
    defer fmt.Println("world")
    fmt.Println("hello")
}

Defer : A defer statement defers the execution of a function until the surrounding function returns. The deferred call's arguments are evaluated immediately, but the function call is not executed until the surrounding function returns.

Sprint

func funcSqrt(x float64) string {
    if x < 0 {
        return funcSqrt(-x) + "i"
    }
    return fmt.Sprint(math.Sqrt(x))
}

Switch

func main() {
  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.\n", os)
  }
}

Switch Operations

func main() {
  fmt.Println("When's Saturday?")
  today := time.Now().Weekday()
  fmt.Print(time.Saturday,"\n",today,"\n")
  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.")
  }
}

Tagless switch

switch {
case t.Hour() < 12:
  fmt.Println("Good morning!")
case t.Hour() < 17:
  fmt.Println("Good afternoon.")
default:
  fmt.Println("Good evening.")
}

Function Closure

Go functions may be closures. A closure is a function value that references variables from outside its body. The function may access and assign to the referenced variables; in this sense the function is "bound" to the variables. hence the function becomes static in some sense and its lifetime is that of the variable it gets binded to. also the internal variable of the func also lives as long as the binded variable

package main

import "fmt"

func adder() func(int) int {
    sum := 0
    return func(x int) int {
        sum += x
        return sum
    }
}

func main() {
    pos, neg := adder(), adder()
    for i := 0; i < 10; i++ {
        fmt.Println(
            pos(i),
            neg(-2*i),
        )
    }
}

panic and recover

Earlier, we created a function that called the panic function to cause a runtime error. We can handle a runtime panic with the built-in recover function. recover stops the panic and returns the value that was passed to the call to panic . We might be tempted to recover from a panic like this:

package main
import "fmt"
func main() {
    panic("PANIC")
    str := recover() // this will never happen
    fmt.Println(str)
}

But the call to recover will never happen in this case, because the call to panic imme‐ diately stops execution of the function. Instead, we have to pair it with defer :

package main
import "fmt"
func main() {
    defer func() {
        str := recover()
        fmt.Println(str)
    }()
    panic("PANIC")
}

Iota basic example

The iota keyword represents successive integer constants 0, 1, 2,…
It resets to 0 whenever the word const appears in the source code,
and increments after each const specification.

const (
    C0 = iota
    C1 = iota
    C2 = iota
)
fmt.Println(C0, C1, C2) // "0 1 2"

This can be simplified to

const (
    C0 = iota
    C1
    C2
)

Here we rely on the fact that expressions are implicitly repeated in a parenthesized const declaration – this indicates a repetition of the preceding expression and its type.

Start from one To start a list of constants at 1 instead of 0, you can use iota in an arithmetic expression.

const (
    C1 = iota + 1
    C2
    C3
)
fmt.Println(C1, C2, C3) // "1 2 3"

Skip value You can use the blank identifier to skip a value in a list of constants.

const (
    C1 = iota + 1
    _
    C3
    C4
)
fmt.Println(C1, C3, C4) // "1 3 4"

Complete enum type with strings [best practice] Here’s an idiomatic way to implement an enumerated type:

create a new integer type,
list its values using iota,
give the type a String function.
type Direction int

const (
    North Direction = iota
    East
    South
    West
)

func (d Direction) String() string {
    return [...]string{"North", "East", "South", "West"}[d]
}

In use:

var d Direction = North
fmt.Print(d)
switch d {
case North:
    fmt.Println(" goes up.")
case South:
    fmt.Println(" goes down.")
default:
    fmt.Println(" stays put.")
}
// Output: North goes up.