编写深度为d的嵌套迭代器

Question

How to realize a nested iterator that takes a depth argument. A simple iterator would be when depth = 1. it is a simple iterator which runs like a simple for loop.

func Iter () chan int {
    ch := make(chan int);
    go func () {
        for i := 1; i < 60; i++ {
            ch <- i
        }
        close(ch)
    } ();
    return ch
}

Output is 1,2,3...59

For depth = 2 Output would be "1,1" "1,2" ... "1,59" "2,1" ... "59,59"

For depth = 3 Output would be "1,1,1" ... "59,59,59"

I want to avoid a nested for loop. What is the solution here ?

Answer 1

I don't know if it is possible to avoid nested loops, but one solution is to use a pipeline of channels. For example:

const ITER_N = 60

// ----------------

func _goFunc1(out chan string) {
    for i := 1; i < ITER_N; i++ {
        out <- fmt.Sprintf("%d", i)
    }
    close(out)
}

func _goFuncN(in chan string, out chan string) {
    for j := range in {
        for i := 1; i < ITER_N; i++ {
            out <- fmt.Sprintf("%s,%d", j, i)
        }
    }
    close(out)
}

// ----------------

// create the pipeline
func IterDepth(d int) chan string {
    c1 := make(chan string)
    go _goFunc1(c1)

    var c2 chan string
    for ; d > 1; d-- {
        c2 = make(chan string)
        go _goFuncN(c1, c2)
        c1 = c2

    }
    return c1
}

You can test it with:

func main() {
    c := IterDepth(2)

    for i := range c {
        fmt.Println(i)
    }
}