Collections and Composite Types

Appending to Slices

Slices can grow with append, returning an updated slice value.

append `append` returns a slice that includes the added value.

Appending to Slices

nextScore
slices_append.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var nextScore = 95
	scores := []int{82, 91}
	updated := append(scores, nextScore)

	fmt.Println("before=", scores)
	fmt.Println("after=", updated)
	fmt.Println("length=", len(updated))
}

package main

import "fmt"

func main() {
	var nextScore = 70
	scores := []int{82, 91}
	updated := append(scores, nextScore)

	fmt.Println("before=", scores)
	fmt.Println("after=", updated)
	fmt.Println("length=", len(updated))
}

package main

import "fmt"

func main() {
	var nextScore = 100
	scores := []int{82, 91}
	updated := append(scores, nextScore)

	fmt.Println("before=", scores)
	fmt.Println("after=", updated)
	fmt.Println("length=", len(updated))
}

  1. nextScore ← 95, scores ← []int{82, 91}, updated ← []int{82, 91, 95}

    5func main() {6  var nextScore→ 95 = 95 //@nextScore=70, 1007  scores→ []int{82, 91} := []int{82, 91}8  updated→ []int{82, 91, 95} := append(scores[]int{82, 91}, nextScore95)910  fmt.Println("before=", scores[]int{82, 91})11  fmt.Println("after=", updated[]int{82, 91, 95})12  fmt.Println("length=", len(updated[]int{82, 91, 95}))13}
    outputbefore= [82 91]
after= [82 91 95]
length= 3

  1. nextScore ← 70, scores ← []int{82, 91}, updated ← []int{82, 91, 70}

    5func main() {6  var nextScore→ 70 = 707  scores→ []int{82, 91} := []int{82, 91}8  updated→ []int{82, 91, 70} := append(scores[]int{82, 91}, nextScore70)910  fmt.Println("before=", scores[]int{82, 91})11  fmt.Println("after=", updated[]int{82, 91, 70})12  fmt.Println("length=", len(updated[]int{82, 91, 70}))13}
    outputbefore= [82 91]
after= [82 91 70]
length= 3

  1. nextScore ← 100, scores ← []int{82, 91}, updated ← []int{82, 91, 100}

    5func main() {6  var nextScore→ 100 = 1007  scores→ []int{82, 91} := []int{82, 91}8  updated→ []int{82, 91, 100} := append(scores[]int{82, 91}, nextScore100)910  fmt.Println("before=", scores[]int{82, 91})11  fmt.Println("after=", updated[]int{82, 91, 100})12  fmt.Println("length=", len(updated[]int{82, 91, 100}))13}
    outputbefore= [82 91]
after= [82 91 100]
length= 3

Append One Score

  1. scores starts as 82, 91.
  2. nextScore is 95.
  3. append(scores, nextScore) returns an updated slice.
  4. The updated length is 3. | Step | Values | | --- | --- | | before | [82 91] | | appended value | 95 | | after | [82 91 95] |

Exercise: slices_append.go

Append one score to a slice and print the before slice, after slice, and length