One of the new features introduced in PHP 5.5 is the generator syntax. The docs on php.net define it as:

A generator function looks just like a normal function, except that instead of returning a value, a generator yields as many values as it needs to.

As an example the following 2 functions would return the same results. 

<?php
$people = [
    ['firstName' => 'Jon', 'lastName' => 'Doe'],
    ['firstName' => 'Jane', 'lastName' => 'Doe'],
    ['firstName' => 'Travis', 'lastName' => 'Doe'],
];

function arrayNames($people)
{
    $names = [];
    foreach ($people as $person) {
        $names[] = implode(' ', $person);
    }
    return $names;
}

function yieldNames($people)
{
    foreach ($people as $person) {
        yield implode(' ', $person);
    }
}

foreach (arrayNames($people) as $name) {
    echo $name . PHP_EOL;
}

foreach (yieldNames($people) as $name) {
    echo $name . PHP_EOL;
}
?>

So yea, less code?

There you have it. You can now write less code in all your iterations, and have all the free time in the world to tackle the important things in like like knitting… But wait. There has to be more to it then that.

There is and it’s Memory Usage

Among the benefits of using generators the one that stood out to me the most what the promise of decreased memory usage. Reducing the memory footprint helps free resources to serve more requests and squeeze the most out of your hardware. For the purpose of this experiment I would like to put that to the test.

Testing it out

To check the difference in memory usage I wrote a simple test. First I went to http://www.json-generator.com/ and generated some sample json data. Then I wrote a quick script that would allow me to test out the two approaches and see how much a difference there is. Here is the gist of it:

Results

The sample json data I used contained around 100 records and I ran the test 5 times each running PHP 5.5.9 on Ubuntu 14.04. Note: I didn’t include the individual results because they all were the same.

Array test result

$ php TestYield.php array
Running [array] test
Start Memory Usage: 1087592
After test function: 1112744 Diff: 24.56 kb
................................................................
.....................................
After loop: 1113416 Diff: 25.22 kb

Yield test result

$ php TestYield.php yield
Running [yield] test
Start Memory Usage: 1087592
After test function: 1088800 Diff: 1.18 kb
.................................................................
....................................
After loop: 1088984 Diff: 1.36 kb

Observations

Dumping values

One thing I noticed in testing this out is that running var_dump or print_r on the yieldNames function returns an empty Generator Object. This may be cumbersome at some point when debugging as so far the only means I have found to dump the content is to loop over the results.

Using return

Returning any value from a generator will result in a compile error. The recommendation from php.net is:

A generator cannot return a value: doing so will result in a compile error. An empty return statement is valid syntax within a generator and it will terminate the generator.

Conclusion

It does indeed appear that using PHP 5.5 generators has an impact on memory usage. This test shows that using generators consumes about 4% of the memory array does. Now I’m sure YMMV and there could be other things that effect these results but as an example it does look promising. Once PHP 5.5 usage is more universal I would expect libraries like Zend Framework would benefit greatly from these optimizations.