What happens to a slice in Go if its capacity is 8 and we try to add a ninth element?

In Go, a slice is a structure that contains a pointer to an array, a length (len), and a capacity (capacity). Capacity is the maximum number of elements that the current array can hold.

If a slice has a capacity of 8, and we try to add a ninth element using append, the following happens:

• Go allocates a new array with increased capacity (usually twice the current, so about 16).
• It copies all existing elements to the new array.
• It adds the new element.
• It returns a new slice pointing to this new array with an updated length and capacity.

Thus, append automatically expands the slice when capacity is exceeded, ensuring dynamic resizing.

Example:

s := make([]int, 8, 8) // length and capacity 8
s = append(s, 9)        // add the 9th element
fmt.Println(len(s))     // 9
fmt.Println(cap(s))     // >= 9, usually 16