Go에서 반복자를 만드는 가장 좋은 방법은 무엇입니까: 채널, 클로저 또는 명명된 유형?

package main

import "fmt"

func main() {
    gen := newEven()
    fmt.Println(gen())
    fmt.Println(gen())
    fmt.Println(gen())
    gen = nil // release for garbage collection
}

func newEven() func() int {
    n := 0
    return func() int {
        n += 2
        return n
    }
}

package main

import "fmt"

func main() {
    gen := even(0)
    fmt.Println(gen.next())
    fmt.Println(gen.next())
    fmt.Println(gen.next())
}

type even int

func (e *even) next() int {
    *e += 2
    return int(*e)
}

package main

import "fmt"

func main() {
    gen := mapInt(newEven(), square)
    fmt.Println(gen())
    fmt.Println(gen())
    fmt.Println(gen())
    gen = nil // release for garbage collection
}

type intGen func() int

func newEven() intGen {
    n := 0
    return func() int {
        n += 2
        return n
    }
}

func mapInt(g intGen, f func(int) int) intGen {
    return func() int {
        return f(g())
    }
}

func square(i int) int {
    return i * i
}