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Puzzle 10 Explanation: Simple Append

Puzzle 10 Explanation: Simple Append

Understand how to use append in Go.

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Try it yourself

Try executing the code below to see the result for yourself.

Go (1.16.5)
package main
import (
	"fmt"
)
func main() {
	a := []int{1, 2, 3}
	b := append(a[:1], 10)
	fmt.Printf("a=%v, b=%v\n", a, b)
}

Explanation

We’ll need to dig a bit into how slices are implemented and how append works to understand why we seed this output.

If we look at src/runtime/slice.go in the Go source code, we will see:

type slice struct {
    array unsafe.Pointer
    len int
    cap int
}

Above, slice is a struct with three fields. We use array as a pointer to the underlying array that holds the data. Next, ...