What is the key difference between slices and arrays in Go?

Slices are dynamically resizable views of arrays.

Characteristic	Array	Slice
Size	Fixed, determined at creation	Dynamic, can change
Type	[n]T (where n is size, T is type)	[]T (where T is type)
Passing to functions	By value (copy)	By reference to underlying array, passing head, len, and cap (effectively, a new SliceHeader structure with copies of these fields)
Creation	var a [5]int or b := [3]string{"a", "b", "c"}	var s []int or t := []int{1, 2, 3} or u := make([]int, 5)
Performance	More predictable due to fixed size, may perform better with small sizes	May have overhead when resizing (reallocating underlying array)

// Array example
var arr [3]int = [3]int{1, 2, 3}

// Slice example created from array
slice := arr[1:] // slice {2, 3}

// Creating a slice
s := []int{10, 20, 30} // underlying array {10, 20, 30}, len = 3, cap = 3

// Modifying the slice
s = append(s, 40) // now s {10, 20, 30, 40}. If capacity is exceeded, a new underlying array is created, len = 4, cap = 6 (usually doubling the capacity).

// Modifying an element of the slice changes the underlying array
slice[0] = 99 // arr now {1, 99, 3}
fmt.Println(arr)