What are the advantages of using a "Generator" (Yield) in PHP?

Question

As of PHP 5.5, the Generator. It can be used within a function from the keyword yield.

In the manual, we have an example where one is compared to function range(0, 1000000) (that theoretically would spend 100MB of memory) and an implementation of xrange through the generators (that would reduce memory consumption to 1 Kilobyte).

Example of the manual:

<?php
function xrange($start, $limit, $step = 1) {
    if ($start < $limit) {
        if ($step <= 0) {
            throw new LogicException('Step must be +ve');
        }

        for ($i = $start; $i <= $limit; $i += $step) {
            yield $i;
        }
    } else {
        if ($step >= 0) {
            throw new LogicException('Step must be -ve');
        }

        for ($i = $start; $i >= $limit; $i += $step) {
            yield $i;
        }
    }
}

/*
 * Note that both range() and xrange() result in the same
 * output below.
 */

echo 'Single digit odd numbers from range():  ';
foreach (range(1, 9, 2) as $number) {
    echo "$number ";
}
echo "\n";

echo 'Single digit odd numbers from xrange(): ';
foreach (xrange(1, 9, 2) as $number) {
    echo "$number ";
}
?>

In addition to the advantage of saving this memory and simplifying the use of a iterator, what are the other advantages of using the Generator in PHP?

Answer 1

In the background generators are not to save memory. This is another welcome side effect. They exist to create data sequences on demand.

His general idea is to be able to better control what happens between the generation of each element of the sequence.

One of the advantages is to produce code with better abstractions. You encapsulate the mechanism of how you get the die within a function and leave another function, probably in a loop, manipulate this data without worrying about how it was obtained. You separate the mechanism from the business rule.

He also allows what’s called Lazy Evaluation where you only compute a sequence item when and if you will actually use it. Without the generator it is very common to generate huge data sequences, probably in lists or arrays, and spend a huge amount of time to generate all the elements and then just actually use some of them and discard the rest. The generator saves memory and processing.

Another use is in the creation of state machine and corollaries since he can maintain status between calls of his executions. He has natural breaks.

The operation of a generator is more or less equal in all languages that have it. I already I answered something about this in C# that has a very sophisticated generator. There are some good examples.

The memory gain is relative. If you need all the generated and used sequence at the same time, there is no gain (if you know what you are doing).

Generators are not great for all cases. They provoke in little overhead. Not that this is a reason not to use it, but if it doesn’t provide a real advantage you have no reason to accept a overhead.