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Exploring and Mastering the Full Go Featureset

Nil Slices

Explore how nil slices in Go differ from empty slices and how functions like len, cap, and append interact with them. Understand performance implications, memory management with slice arrays, and techniques for handling multidimensional or jagged slices.

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Nil slices

Slices don’t have to be checked for nil values and don’t always need to be initialized. Functions such as len, cap, and append work fine on a nil slice:

Go (1.16.5)
package main
import "fmt"
func main() {
    var s []int // nil slice
    fmt.Println(s, len(s), cap(s)) // [] 0 0
    s = append(s, 1)
    fmt.Println(s, len(s), cap(s)) // [1] 1 1
}

An empty slice is not the same thing as a nil slice:

Go (1.16.5)
package main
import "fmt"
func main() {
    var s []int // this is a nil slice
    s2 := []int{} // this is an empty slice
    // looks like the same thing here:
    fmt.Println(s, len(s), cap(s)) // [] 0 0
    fmt.Println(s2, len(s2), cap(s2)) // [] 0 0
    // but s2 is actually allocated somewhere
    fmt.Printf("%p %p", s, s2) // 0x0 0x65ca90(any address)
}

If you care very ...