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In-Reply-To: <CALKiJKqKCML78TCWeB-Tu5hAYPq-4_qT2=tLfyj+D3NiBn9bDw@mail.gmail.com>
Date: Thu, 21 Mar 2019 15:21:35 +0000
Message-ID: <CAMuFt-6eAinA+Kq8UwEkkpv1_HrABKd1_7Wi2vP1t-8Dh=T8dA@mail.gmail.com>
To: Rowan Collins <rowan.collins@gmail.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] RFC Draft: Comprehensions
From: robehickman@gmail.com (Robert Hickman)

> But  $filteredArrayIterator->next() is actually $arrayIterator->next() with
> a built-in if check, so you could also picture it as doing this:
>
> while ( $element = $arrayIterator->nextIf ( someCondition ) ) {
>     $newArray[] = $element;
> }
>

In this case nextIf() would have to be implemented something like:

function nextif($someCondition) {
    foreach($this->iteratorValue as $x) {
        if(<some comparison of $x and $$someCondition) {
             yield $x;
        }
    }
}

iterator_to_array would need an internal loop to pull the values from
the generator. Thus, as far as I can see, the generator implementation
would result in two loops running in lock step, rather than only one
in the eager case.

You do make a good point about the potential for the optimiser to
recognise and automatically deal with such cases however.