Understanding Slice Underlying Array Retrieval in Go

In Go, a slice is a flexible data structure that provides an abstraction over an array. When working with slices, it may be necessary to access the underlying array. This article explains the mechanics behind this process and how to retrieve the reference to the new array.

Let's consider a slice numSlice derived from an array nums as presented in the original question. By default, both numSlice and nums share the same underlying array. However, this underlying array can change when the slice's capacity is exceeded during operations such as appending elements.

To access the underlying array of a slice, a combination of reflect and unsafe can be employed. Here's how:

Using reflect and unsafe

• Use reflect.SliceHeader to obtain the metadata of the slice, including the pointer to the underlying array (hdr.Data).
• Convert this pointer to an array pointer using unsafe.Pointer.

Here's an example adapting the Go documentation:

s := []int{1, 2, 3, 4}
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&s))
data := *(*[4]int)(unsafe.Pointer(hdr.Data))

Note: Due to the use of unsafe, it's essential to handle memory management cautiously.

Additional Resources

For a comprehensive understanding of slice internals, refer to the official Go blog post [here](https://blog.golang.org/go-slices-usage-and-internals).