Slice declaration
- Go course
- Beginner
- Lesson 42/90
- 4 min
Learn to declare dynamic arrays with slices.
Defining slices
A slice is a flexible-length view onto part of an array. Its type has no length: []int.
a := []int{1, 2, 3} // with a literal
b := make([]int, 5) // [0 0 0 0 0]
var c []int // nil slice, len 0
fmt.Println(len(a), len(b), c == nil) // 3 5 trueA slice holds three things: a pointer to the underlying array, a length (len) and a capacity (cap).
nil and empty slices
var s []int is a nil slice; s := []int{} is an empty but non-nil slice. Both have len 0, and range and append work fine on either. The difference shows in JSON: a nil slice encodes as null, an empty one as []. Slices can't be compared with == (only to nil); use slices.Equal to compare contents.
Practice Independent copy
Declare a := []int{1, 2, 3}. Make a copy with b := make([]int, len(a)) and copy(b, a), set b[0] = 99 and print a and b on one line.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func main() {
a := []int{1, 2, 3}
b := make([]int, len(a))
copy(b, a)
b[0] = 99
fmt.Println(a, b)
}Expected output
[1 2 3] [99 2 3]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 After <code>b := a</code> (a is a slice), if <code>b[0] = 99</code>, what is <code>a[0]</code>?
- A panic
- 99; both share the same array Correct answer
- Unchanged
- 0
Explanation: Assigning a slice copies only its header; the underlying array is shared. For an independent copy use copy or slices.Clone.
2 Preset length
puanlar := ____([]int, 3) // [0 0 0]puanlar := make([]int, 3) // [0 0 0]Explanation: make creates a slice of the given length filled with zero values.
3 Definition and result
| Term | Meaning |
|---|---|
[]int{1, 2} |
len 2 |
make([]int, 3) |
[0 0 0] |
var s []int |
nil, len 0 |
[]int{} |
Empty, not nil |