What is the difference between arrays and slices in Go?

Arrays and slices are both ordered sequences, but they work very differently. Arrays are value types with a fixed size baked into their type; slices are reference types that provide a flexible view into an underlying array.

// Array
var arr [5]int                       // [0 0 0 0 0]
arr2 := [3]string{"a", "b", "c"}
arr3 := [...]int{1, 2, 3, 4}         // compiler counts: [4]int

// Slice
s := []int{1, 2, 3}                  // slice literal
s2 := make([]int, 5)                 // len=5, cap=5, all zeros
s3 := make([]int, 3, 10)             // len=3, cap=10

// append — returns a NEW slice (may reallocate backing array)
s = append(s, 4, 5)                  // [1 2 3 4 5]

// Sub-slice — shares backing array!
sub := s[1:4]                        // [2 3 4]
sub[0] = 99                           // changes s[1] too!

// copy — independent backing array
dst := make([]int, len(s))
copy(dst, s)

// nil slice vs empty slice
var nilSlice []int                   // nil — len=0, cap=0
empty := []int{}                     // not nil — len=0, cap=0
fmt.Println(nilSlice == nil)          // true
fmt.Println(empty == nil)             // false

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