kotlin-result/src/main/kotlin/com/mikebull94/result/ResultIterator.kt

package com.mikebull94.result

/**
 * Creates an [Iterator] over the possibly contained [value][Ok.value].
 * The iterator yields one [value][Ok.value] if the [Result] is [Ok], otherwise throws [NoSuchElementException].
 *
 * - Rust: [Result.iter](https://doc.rust-lang.org/std/result/enum.Result.html#method.iter)
 *
 * @return [Iterator] over the possibly contained [value][Ok.value].
 */
fun <V, E> Result<V, E>.iterator(): Iterator<V> {
    return ResultIterator(this)
}

/**
 * Creates a [MutableIterator] over the possibly contained [value][Ok.value].
 * The iterator yields one [value][Ok.value] if the [Result] is [Ok], otherwise throws [NoSuchElementException].
 *
 * - Rust: [Result.iter_mut](https://doc.rust-lang.org/std/result/enum.Result.html#method.iter_mut)
 *
 * @return The [MutableIterator] over the possibly contained [value][Ok.value].
 */
fun <V, E> Result<V, E>.mutableIterator(): MutableIterator<V> {
    return ResultIterator(this)
}

private class ResultIterator<out V, out E>(private val result: Result<V, E>) : MutableIterator<V> {

    /**
     * A flag indicating whether this [Iterator] has [yielded] its [Result].
     */
    private var yielded = false

    /**
     * @return `true` if the [value][Ok.value] is not [yielded] and [Ok], `false` otherwise.
     */
    override fun hasNext(): Boolean {
        if (yielded) {
            return false
        }

        return when (result) {
            is Ok -> true
            is Error -> false
        }
    }

    /**
     * @return The [Result's][Result] [value][Ok.value] if not [yielded] and [Ok].
     * @throws NoSuchElementException if the [Result] is [yielded] or is not [Ok].
     */
    override fun next(): V {
        if (!yielded && result is Ok) {
            yielded = true
            return result.value
        } else {
            throw NoSuchElementException()
        }
    }

    /**
     * Flags this [Iterator] as having [yielded] its [Result].
     */
    override fun remove() {
        yielded = true
    }
}