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November 28, 2021 05:43 am GMT

Using NEW, instead of MAKE, to create slice

As we know, slices in golang are reference types, and hence, need make to initialize them.

func main() {    a := make([]int32, 0)    a = append(a, 10, 20, 30)    fmt.Println(len(a), cap(a), reflect.ValueOf(a).Kind())}>>> 3 4 slice

But, can we use new to make slices? It's meant to be used for value types only. So how can it work here?

Let's see

func main() {    a := new([]int32)}

Does this work? Yes. It does. So what is the difference?

The difference is that this gives you a pointer, as is the case anytime you use new. Thus to actually use it, you have to dereference it everytime.

Example:

func main() {    a := new([]int32)    *a = append(*a, 10, 20, 30)    fmt.Println(len(*a), cap(*a), reflect.ValueOf(*a).Kind())}>>> 3 4 slice

Another simple change you can do is to dereference it immediately after creation. This will save you the effort of dereferencing it every other time.

func main() {    a := *new([]int32)    a = append(a, 10, 20, 30)    fmt.Println(len(a), cap(a), reflect.ValueOf(a).Kind())}>>> 3 4 slice

There's another important concept:

Every time you append to a slice, it gives you a new slice with a different address (though it points to same underlying array)

Let's see this with same example:

func main() {    a := make([]int32, 0)    fmt.Printf("%p
", a)    a = append(a, 10, 20, 30)    fmt.Printf("%p
", a)    a = append(a, 10, 20, 30)    fmt.Printf("%p
", a)    fmt.Println(len(a), cap(a), reflect.ValueOf(a).Kind())}>>> 0x116bea0>>> 0xc0000220e0>>> 0xc00001c100>>> 6 8 slice

You see, all 3 addresses are different.

But, can we keep the addresses same even after append? Well yes!! It's here your NEW approach comes into place. See this:

func main() {    a := new([]int32)    fmt.Printf("%p
", a)    *a = append(*a, 10, 20, 30)    fmt.Printf("%p
", a)    *a = append(*a, 10, 20, 30)    fmt.Printf("%p
", a)    fmt.Println(len(*a), cap(*a), reflect.ValueOf(*a).Kind())}>>> 0xc00011c030>>> 0xc00011c030>>> 0xc00011c030>>> 6 8 slice

You see? All 3 addresses remain same!!!

That's all folks for now

Original Link: https://dev.to/freakynit/using-new-instead-of-make-to-create-slice-17bl

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