go - How to collect values from N goroutines executed in a specific order?

Question

Below is a struct of type Stuff. It has three ints. A Number, its Double and its Power. Let's pretend that calculating the double and power of a given list of ints is an expensive computation.

type Stuff struct {
    Number int
    Double int
    Power  int
}

func main() {
    nums := []int{2, 3, 4} // given numbers
    stuff := []Stuff{}     // struct of stuff with transformed ints

    double := make(chan int)
    power := make(chan int)

    for _, i := range nums {
        go doubleNumber(i, double)
        go powerNumber(i, power)
    }

    // How do I get the values back in the right order?

    fmt.Println(stuff)
}

func doubleNumber(i int, c chan int) {
    c <- i + i
}

func powerNumber(i int, c chan int) {
    c <- i * i
}

The result of fmt.Println(stuff) should be the same as if stuff was initialized like:

stuff := []Stuff{
    {Number: 2, Double: 4, Power: 4}
    {Number: 3, Double: 6, Power: 9}
    {Number: 4, Double: 8, Power: 16}
}

I know I can use <- double and <- power to collect values from the channels, but I don't know what double / powers belong to what numbers.

Answer 1

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