PHP Generators
Generators provide an easy way to implement simple iterators without the overhead or complexity of implementing a class that implements the Iterator interface.
A generator allows you to write code that uses foreach to iterate over a set of data without needing to build an array in memory, which may cause you to exceed a memory limit.
1. The yield Keyword
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.
When a generator function is called, it returns an object that can be iterated over.
function simpleGenerator() {
yield 1;
yield 2;
yield 3;
}
foreach (simpleGenerator() as $value) {
echo $value . "\n";
}2. Why Use Generators? (Memory Efficiency)
The primary benefit is memory usage. If you need to iterate over a large range of numbers or lines in a file, an array stores them all in memory at once. A generator yields them one by one.
Using an Array (High Memory)
function getRange($max) {
$array = [];
for ($i = 0; $i < $max; $i++) {
$array[] = $i;
}
return $array;
}Using a Generator (Low Memory)
function getRangeGenerator($max) {
for ($i = 0; $i < $max; $i++) {
yield $i;
}
}
// This uses constant memory regardless of $max
foreach (getRangeGenerator(1000000) as $number) { ... }