00_README.md

Go Slices Advanced Concepts

This Gist contains the code examples from the blog post Mastering Slices in Go: Deep Dive into Nil vs Empty Slices, Capacity, and Length.

01.go

package main

import (
    "fmt"
)

func main() {
    // Declaring a nil slice
    var s []int
    printSliceInfo("s", s)

    // Declaring an empty slice
    t := []int{}
    printSliceInfo("t", t)

    // Declaring a slice with length 5
    u := make([]int, 5)
    printSliceInfo("u", u)

    // Declaring a slice with length 0 but capacity 5
    v := make([]int, 0, 5)
    printSliceInfo("v", v)
}

func printSliceInfo(name string, s []int) {
    fmt.Printf("%s: len=%d cap=%d nil=%t %v\n", name, len(s), cap(s), s == nil, s)
}

02.go

package main

import (
    "fmt"
)

func main() {
    // Create a slice with length 5
    u := make([]int, 5)
    printSliceInfo("u", u)

    // Create a slice with length 0 but capacity 5
    v := make([]int, 0, 5)
    printSliceInfo("v", v)

    // Appending to slices
    v = append(v, 10)
    printSliceInfo("v after append", v)

    // Appending beyond capacity
    v = append(v, 20, 30, 40, 50, 60)
    printSliceInfo("v after more appends", v)
}

func printSliceInfo(name string, s []int) {
    fmt.Printf("%s: len=%d cap=%d %v\n", name, len(s), cap(s), s)
}

03.go

package main

import (
    "encoding/json"
    "fmt"
)

func main() {
    var s []int // nil slice
    t := []int{} // empty slice

    sj, _ := json.Marshal(s)
    tj, _ := json.Marshal(t)

    fmt.Printf("Nil slice as JSON: %s\n", sj)
    fmt.Printf("Empty slice as JSON: %s\n", tj)
}

04.go

package main

import "fmt"

func main() {
    // Create an array with three elements
    a := [3]int{1, 2, 3}
    // Create a slice from the first element of the array
    b := a[0:1]

    fmt.Printf("Slice b - Length: %d, Capacity: %d\n", len(b), cap(b)) // Output: Length: 1, Capacity: 3
}

05.go

package main

import "fmt"

func main() {
    // Create an array with three elements
    a := [3]int{1, 2, 3}
    // Create a slice from the first element of the array
    b := a[0:1]
    // Create a slice from slice b
    c := b[0:2]

    fmt.Println("Slice c:", c) // Output: Slice c: [1 2]
    fmt.Printf("Slice c - Length: %d, Capacity: %d\n", len(c), cap(c)) // Output: Length: 2, Capacity: 3
}

06.go

package main

import "fmt"

func main() {
    // Create an array with three elements
    a := [3]int{1, 2, 3}
    // Create a slice with length and capacity controlled by the three-index slice operator
    d := a[0:1:1]

    fmt.Println("Slice d:", d) // Output: Slice d: [1]
    fmt.Printf("Slice d - Length: %d, Capacity: %d\n", len(d), cap(d)) // Output: Length: 1, Capacity: 1
}

07.go

package main

import "fmt"

func main() {
    // Create an array with three elements
    a := [3]int{1, 2, 3}
    // Create a slice from the first two elements of the array
    c := a[0:2]

    fmt.Println("Before append, Array a:", a) // Output: Before append, Array a: [1 2 3]
    fmt.Println("Before append, Slice c:", c) // Output: Before append, Slice c: [1 2]

    // Append to slice c
    c = append(c, 5)

    fmt.Println("After append, Array a:", a) // Output: After append, Array a: [1 2 5]
    fmt.Println("After append, Slice c:", c) // Output: After append, Slice c: [1 2 5]
}

08.go

package main

import "fmt"

func main() {
    // Create an array with three elements
    a := [3]int{1, 2, 3}
    // Create a slice with limited capacity
    c := a[0:2:2]

    fmt.Println("Before append, Array a:", a) // Output: Before append, Array a: [1 2 3]
    fmt.Println("Before append, Slice c:", c) // Output: Before append, Slice c: [1 2]

    // Append to slice c
    c = append(c, 5)

    fmt.Println("After append, Array a:", a) // Output: After append, Array a: [1 2 3]
    fmt.Println("After append, Slice c:", c) // Output: After append, Slice c: [1 2 5]
}