Slice output

This example will help to directly see the behavior of various slice operations.

package main

import "fmt"

type Slc struct {
    A, B, C []int
}

func (s *Slc) Print(logName string) {
    fmt.Println(logName, "-")
    fmt.Println("A", ":", s.A, " | len", len(s.A), " | cap", cap(s.A))
    fmt.Println("B", ":", s.B, "| len", len(s.B), "| cap", cap(s.B))
    fmt.Println("C", ":", s.C, "| len", len(s.C), "| cap", cap(s.C))
    fmt.Println()
}

func main() {
    slc := Slc{
        A: []int{1, 2},
        B: []int{3, 4},
    }
    slc.Print("initial")

    slc.C = slc.A
    slc.Print("after setting A to C")

    slc.A[0] = 12
    slc.Print("after setting A[0] to 12")

    copy(slc.A, slc.B)
    slc.Print("after copy B to C")

    slc.A[0] = 14
    slc.Print("after setting A[0] to 14")

    slc.A[0] = 15
    slc.Print("after setting C[0] to 15")

    slc.B[0] = 11
    slc.Print("after setting B[0] to 11")

    // When we append 5 to A, a new array is created
    slc.A = append(slc.A, 5)
    slc.Print("after appending 5 to A")

    slc.A[0] = 10
    slc.Print("after setting A[0] to 10")

    slc.A = slc.A[:1]
    slc.Print("after setting A to slc.A[:1]")

    slc.A = []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    slc.Print("after setting A to {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}")

    slc.A = slc.A[0:len(slc.A)]
    slc.Print("after setting A to slc.A[0:len(slc.A)]")

    slc.A = slc.A[0:5]
    slc.Print("after setting A to slc.A[0:5]")

    slc.A = slc.A[2:4]
    slc.Print("after setting A to slc.A[2:4]")
}

Output :

initial -
A : [1 2]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [] | len 0 | cap 0

after setting A to C -
A : [1 2]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [1 2] | len 2 | cap 2

after setting A[0] to 12 -
A : [12 2]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [12 2] | len 2 | cap 2

after copy B to C -
A : [3 4]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [3 4] | len 2 | cap 2

after setting A[0] to 14 -
A : [14 4]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [14 4] | len 2 | cap 2

after setting C[0] to 15 -
A : [15 4]  | len 2  | cap 2
B : [3 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting B[0] to 11 -
A : [15 4]  | len 2  | cap 2
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after appending 5 to A -
A : [15 4 5]  | len 3  | cap 4
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A[0] to 10 -
A : [10 4 5]  | len 3  | cap 4
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A to slc.A[:1] -
A : [10]  | len 1  | cap 4
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A to {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10} -
A : [0 1 2 3 4 5 6 7 8 9 10]  | len 11  | cap 11
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A to slc.A[0:len(slc.A)] -
A : [0 1 2 3 4 5 6 7 8 9 10]  | len 11  | cap 11
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A to slc.A[0:5] -
A : [0 1 2 3 4]  | len 5  | cap 11
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2

after setting A to slc.A[2:4] -
A : [2 3]  | len 2  | cap 9
B : [11 4] | len 2 | cap 2
C : [15 4] | len 2 | cap 2