How is a slice passed to a function in a programming language?

In Go, a slice is passed to a function by value, but the slice contains a pointer to an array, along with its length and capacity. This means that when passing a slice to a function, the slice structure is copied, but the underlying array data it points to is not copied.

As a result, modifications to the elements of the slice inside the function are reflected in the original array, but changes to the slice itself (for example, assigning a new slice) do not affect the external slice.

Example:

package main
import "fmt"

func modifySlice(s []int) {
    s[0] = 100       // will change the element in the original array
    s = append(s, 200) // will change the local slice, but not the external one
}

func main() {
    s := []int{1, 2, 3}
    modifySlice(s)
    fmt.Println(s) // Will output: [100 2 3]
}

Thus, a slice is passed by value, but due to the internal pointer, changes to elements are visible outside the function.