for the protection from the leaking of resources see RFC https://wiki.php.net/rfc/generators#closing_a_generatorand use finnalysample codefunction getLines($file) {    $f = fopen($file, 'r');    try {        while ($line = fgets($f)) {            yield $line;        }    } finally {        fclose($f);    }}foreach (getLines("file.txt") as $n => $line) {    if ($n > 5) break;    echo $line;}

Bear in mind that execution of a generator function is postponed until iteration over its result (the Generator object) begins. This might confuse one if the result of a generator is assigned to a variable instead of immediate iteration.<?php$some_state = 'initial';function gen() {    global $some_state;     echo "gen() execution start\n";    $some_state = "changed";    yield 1;    yield 2;}function peek_state() {    global $some_state;    echo "\$some_state = $some_state\n";}echo "calling gen()...\n";$result = gen();echo "gen() was called\n";peek_state();echo "iterating...\n";foreach ($result as $val) {    echo "iteration: $val\n";    peek_state();}?>If you need to perform some action when the function is called and before the result is used, you'll have to wrap your generator in another function.<?php/**  * @return Generator  */function some_generator() {    global $some_state;    $some_state = "changed";    return gen();}?>

In addition to the note of "montoriusz at gmail dot com": https://www.php.net/manual/en/language.generators.overview.php#119275"If you need to perform some action when the function is called and before the result is used, you'll have to wrap your generator in another function."You can use Generator::rewind instead (https://www.php.net/manual/en/generator.rewind.php)Sample code:<?php/** function/generator definition **/echo "calling gen()...\n";$result = gen();$result->rewind();echo "gen() was called\n";/** iteration **/?>

Here's how to detect loop breaks, and how to handle or cleanup after an interruption.<?php    function generator()    {        $complete = false;        try {            while (($result = some_function())) {                yield $result;            }            $complete = true;        } finally {            if (!$complete) {                // cleanup when loop breaks             } else {                // cleanup when loop completes            }        }        // Do something only after loop completes    }?>

Abstract test.<?php$start_time=microtime(true);$array = array();$result = '';for($count=1000000; $count--;){  $array[]=$count/2;}foreach($array as $val){  $val += 145.56;  $result .= $val;}$end_time=microtime(true);echo "time: ", bcsub($end_time, $start_time, 4), "\n";echo "memory (byte): ", memory_get_peak_usage(true), "\n";?><?php$start_time=microtime(true);$result = '';function it(){  for($count=1000000; $count--;)  {    yield $count/2;  }}foreach(it() as $val){  $val += 145.56;  $result .= $val;}$end_time=microtime(true);echo "time: ", bcsub($end_time, $start_time, 4), "\n";echo "memory (byte): ", memory_get_peak_usage(true), "\n";?>Result:----------------------------------           |  time  | memory, mb |----------------------------------| not gen  | 2.1216 | 89.25      ||---------------------------------| with gen | 6.1963 | 8.75       ||---------------------------------| diff     | < 192% | > 90%      |----------------------------------

Same example, different results:----------------------------------           |  time  | memory, mb |----------------------------------| not gen  | 0.7589 | 146.75     ||---------------------------------| with gen | 0.7469 | 8.75       ||---------------------------------Time in results varying from 6.5 to 7.8 on both examples.So no real drawbacks concerning processing speed.