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array declaration var elements [4]int

func main() { a := [4]int{1, 2, 3, 4} println("a addr:", &a) for i := range a { print("Value: ", a[i]) println(" Address:", &a[i]) } }

on 64bit architecture, each int = 8 bytes func main() { a := [4]int{1, 2, 3, 4} println("a addr:", &a) for i := range a { print("Value: ", a[i]) println(" Address:", &a[i]) } } a addr: 0x220822bf20 Value: 1 IndexAddr: 0x220822bf20 Value: 2 IndexAddr: 0x220822bf28 Value: 3 IndexAddr: 0x220822bf30 Value: 4 IndexAddr: 0x220822bf38

arrays are contiguous in memory

No content

CPU cache

Pass by value

In Go, everything is pass by value. When we pass an array as an argument, we pass a copy of the array not a reference to the array. package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(names) println(names[0]) } func f1(a [4]string) { a[0] = "marie" }

1. A copy of names is made when f1 is called 1 package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(names) println(names[0]) } func f1(a [4]string) { a[0] = "marie" }

2. The copy of names is assigned to local var a 1 package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(names) println(names[0]) } func f1(a [4]string) { a[0] = "marie" } 2

3. We make a change to the copy 3 2 1 package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(names) println(names[0]) } func f1(a [4]string) { a[0] = "marie" }

3 2 1 package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(names) println(names[0]) } func f1(a [4]string) { a[0] = "marie" } // ada

call stack

Pointers

If we want to share names with f1 so f1 can modify it, then we pass the address of names to f1. package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(&names) println(names[0]) } func f1(a *[4]string) { a[0] = "marie" }

1. Pass the address of names package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(&names) println(names[0]) } func f1(a *[4]string) { a[0] = "marie" } 1

2. f1 accepts a pointer variable package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(&names) println(names[0]) } func f1(a *[4]string) { a[0] = "marie" } 2 1

3. Changes to a update the array that a points to, names. package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(&names) println(names[0]) } func f1(a *[4]string) { a[0] = "marie" } 3 2 1

package main func main() { names := [4]string {"ada", "lovelace", "tom", "jerry"} f1(&names) println(names[0]) } func f1(a *[4]string) { a[0] = "marie" } 3 2 1 // marie

call stack using a pointer

the Go compiler likes to optimise all the things!

func main() { a := [4]int{1, 2, 3, 4} println("a addr:", &a) for i := range a { print("Value: ", a[i]) println(" Address:", &a[i]) } } print

func main() { a := [4]int{1, 2, 3, 4} println("a addr:", &a) for i := range a { print("Value: ", a[i]) println(" Address:", &a[i]) } } print func main() { a := [4]int{1, 2, 3, 4} println("a addr:", &a) for i := range a { print("Value: ", a[i]) println(" Address:", &a[i]) } } import "fmt" func main() { a := [4]int{1, 2, 3, 4} fmt.Printf("a addr: %p \n", &a) for i := range a { fmt.Printf("V: %v A: %p \n", a[i], &a[i]) } } import "fmt" func main() { a := [4]int{1, 2, 3, 4} fmt.Printf("a addr: %p \n", &a) for i := range a { fmt.Printf("V: %v A: %p \n", a[i], &a[i]) } } fmt.Print

1. escape analysis go build -gcflags=-m main.go:6: moved to heap: a main.go:8: &a escapes to heap main.go:11: &a[i] escapes to heap main.go:8: main ... argument does not escape main.go:11: main ... argument does not escape with ft.Printf

1. inlining func main() { names := [2]string{"ada", "lovelace"} f1(names) println(names[0]) } func f1(a [2]string) { a[0] = "marie" }

inlining func main() { names := [2]string{"ada", "lovelace"} f1(names) println(names[0]) } func f1(a [2]string) { a[0] = "marie" // Do this to prevent inlining. var x int fmt.Sprintf("Prevent Inlining: %d", x) }

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