How to insert a new element into the middle of a dynamic array (layer)?

In Go, to insert a new element into the middle of a slice, you need to create a new slice by combining the parts before and after the insertion point, along with the element to insert. For example, to insert element x at position i in slice s:

s = append(s[:i], append([]T{x}, s[i:]...)...)

Here, T is the element type of the slice. This method works as follows:

1. Take a slice of the beginning up to position i (s[:i])
2. Create a slice with the element x ([]T{x})
3. Take a slice from position i to the end (s[i:])
4. Append the element slice and the tail slice
5. Append everything to the start

Example:

s := []int{1, 2, 4, 5}
x := 3
i := 2
s = append(s[:i], append([]int{x}, s[i:]...)...)
// s now: [1 2 3 4 5]

This is the standard way to insert into the middle of a slice in Go.