How Can I Idiomatically Implement Iterators in Go?

Is There an Idiomatic Iterator Implementation in Go?

Channels, reminiscent of iterators, offer iteration via the range keyword. However, the inability to break out of such loops without creating goroutine leaks limits their utility. Seeking a more idiomatic iterator pattern, developers have posed questions about how to iterate expressively and combine iterators using operators like map, filter, and reduce.

Closure-Based Approach

Despite the handiness of channels, closures often prove more suitable. Closures allow the creation of iterators that generate values in a sequential manner. Here's an example of creating an iterator for even numbers using a closure:

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

Method-Based Approach

If closures aren't to your liking, you can employ a named type with a method:

type even int

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

Tradeoffs and Chaining

The choice between closures and methods involves tradeoffs. Closures are more flexible, while methods provide a more explicit structure.

Chaining is straightforward in Go thanks to the first-class nature of functions. The following example demonstrates how to chain an even number generator with a squaring function:

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

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

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