The Go Programming Language Specification
Array types
An array is a numbered sequence of elements of a single type, called
the element type. The number of elements is called the length and is
never negative.
The length is part of the array's type; it must evaluate to a
non-negative constant representable by a value of type int. The length
of array a can be discovered using the built-in function len. The
elements can be addressed by integer indices 0 through len(a)-1.
Slice types
A slice is a descriptor for a contiguous segment of an underlying
array and provides access to a numbered sequence of elements from that
array. A slice type denotes the set of all slices of arrays of its
element type. The value of an uninitialized slice is nil.
Like arrays, slices are indexable and have a length. The length of a
slice s can be discovered by the built-in function len; unlike with
arrays it may change during execution. The elements can be addressed
by integer indices 0 through len(s)-1. The slice index of a given
element may be less than the index of the same element in the
underlying array.
A slice, once initialized, is always associated with an underlying
array that holds its elements. A slice therefore shares storage with
its array and with other slices of the same array; by contrast,
distinct arrays always represent distinct storage.
The array underlying a slice may extend past the end of the slice. The
capacity is a measure of that extent: it is the sum of the length of
the slice and the length of the array beyond the slice; a slice of
length up to that capacity can be created by slicing a new one from
the original slice. The capacity of a slice a can be discovered using
the built-in function cap(a).
You should compare Go arrays to Go slices. Assignment copies the array value. Assignment copies the slice descriptor value. The slice descriptor is a struct with a length, a capacity, and a pointer to its underlying slice array.
type slice struct {
array unsafe.Pointer
len int
cap int
}
For example,
package main
import "fmt"
func main() {
// array
var a = [5]int{1, 2, 3, 4, 5}
b := a
b[4] = 100
fmt.Println(a, b)
// slice
var s = []int{1, 2, 3, 4, 5}
t := s
t[4] = 100
fmt.Println(s, t)
}
Playground: https://play.golang.org/p/8eFa1Mod_Kj
Output:
[1 2 3 4 5] [1 2 3 4 100]
[1 2 3 4 100] [1 2 3 4 100]