var s1 []int         // nil slice
s2 := []int{}        // non-nil, empty slice
s3 := make([]int, 0) // non-nil, empty slice

fmt.Println("s1", len(s1), cap(s1), s1 == nil, s1[:], s1[:] == nil)
fmt.Println("s2", len(s2), cap(s2), s2 == nil, s2[:], s2[:] == nil)
fmt.Println("s3", len(s3), cap(s3), s3 == nil, s3[:], s3[:] == nil)

for range s1 {}
for range s2 {}
for range s3 {}

s1 0 0 true [] true
s2 0 0 false [] false
s3 0 0 false [] false

s := make([]int, 0, 100)
fmt.Println("Empty:", len(s) == 0, ", but capacity:", cap(s))

Empty: true , but capacity: 100

type SliceHeader struct {
    Data uintptr
    Len  int
    Cap  int
}

var s1 []int
s2 := []int{}
s3 := make([]int, 0)

fmt.Printf("s1 (addr: %p): %+8vn",
    &s1, *(*reflect.SliceHeader)(unsafe.Pointer(&s1)))
fmt.Printf("s2 (addr: %p): %+8vn",
    &s2, *(*reflect.SliceHeader)(unsafe.Pointer(&s2)))
fmt.Printf("s3 (addr: %p): %+8vn",
    &s3, *(*reflect.SliceHeader)(unsafe.Pointer(&s3)))

s1 (addr: 0x1040a130): {Data:       0 Len:       0 Cap:       0}
s2 (addr: 0x1040a140): {Data: 1535812 Len:       0 Cap:       0}
s3 (addr: 0x1040a150): {Data: 1535812 Len:       0 Cap:       0}

var n []int
n == nil // true

var n []int
len(n) == cap(n) == 0 // true
n = append(n, 123)
len(n) == 1 // true