How Slices Work Internally in Go

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In my previous post, I explained how to work with arrays and use pointers with arrays.
Now let's learn about slices in go.

What is Slices

Slices are dynamic arrays.

Slices use pointers to refer to the underlying array.

Here is how you can create slices.

How to create slices

Initialize array and create slice from it.

For creating slice from array, we use [start:end] notation.

start is the starting index of the slice.

end is the ending index of the slice.

import "fmt"

func main() {
    s := [5]int{10, 20, 30, 40,50}
    fmt.Println(s)
    var s1 []int = s[1:3]
    fmt.Println(s1)
}

Output:

[10 20 30 40 50]
[20 30]

How Slices Work Internally

Slices will be having 3 components.

1. Pointer to the underlying array.
2. Length of the slice.
3. Capacity of the slice.

It is little bit confusing, let's understand with above example.

[10, 20, 30, 40, 50]

Now by above image we can understand how it works internally.

Conclusion

In this we learned about slice data type and how it works internally.

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Comments

[Clara Bennett]

Nice overview of slice internals! One thing worth mentioning is the gotcha with append — when a slice exceeds its capacity, Go allocates a new underlying array. This means two slices that originally shared the same backing array can diverge silently after an append. It's one of those things that trips people up in production when they're mutating slices passed between functions. The diagram really helps make the pointer/length/capacity relationship click.

[Ganesh Kumar]

Thanks for letting me know.
I have started learning in depth on these concepts.

Will surely mention these gotcha in upcoming articles.