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Generators overview

Generators overview

Generators provide an easy way to implement simple without the overhead or complexity of implementing a class that implements the interface. iteratorsIterator

A generator offers a convenient way to provide data to foreach loops without having to build an array in memory ahead of time, which may cause the program to exceed a memory limit or require a considerable amount of processing time to generate. Instead, a generator function can be used, which is the same as a normal , except that instead of ing once, a generator can yield as many times as it needs to in order to provide the values to be iterated over. Like with iterators, random data access is not possible. functionreturn

A simple example of this is to reimplement the function as a generator. The standard function has to generate an array with every value in it and return it, which can result in large arrays: for example, calling will result in well over 100 MB of memory being used. range``range

As an alternative, we can implement an generator, which will only ever need enough memory to create an object and track the current state of the generator internally, which turns out to be less than 1 kilobyte. xrange()``Iterator

Voorbeeld: Implementing as a generator

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

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

        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 ";
}
?>

Single digit odd numbers from range():  1 3 5 7 9
Single digit odd numbers from xrange(): 1 3 5 7 9

Generator objects

When a generator function is called, a new object of the
internal  class is returned. This object
implements the  interface in much the same
way as a forward-only iterator object would, and provides methods that can
be called to manipulate the state of the generator, including sending
values to and returning values from it.

Generator``Iterator

Volgende Generator syntax →

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