Modern PHP includes Generators, which let you work with large datasets without using too much memory. Instead of building a huge array and then looping through it, a Generator uses yield to return one item at a time. This keeps only the current value in memory.
Example: Generating Numbers
function getNumbersWithGenerator(int $max): Generator {
for ($i = 1; $i <= $max; $i++) {
yield $i;
}
}
// Only one number is in memory at once:
foreach (getNumbersWithGenerator(1_000_000) as $n) {
// Process $n…
}
If you tried to build an array of one million numbers first, PHP would use a lot of memory. With a Generator, it stays small.
Example: Reading a Large CSV File
function readCsvLineByLine(string $filename): Generator {
if (!is_readable($filename)) {
throw new InvalidArgumentException("Cannot read: $filename");
}
$handle = fopen($filename, 'r');
if (!$handle) {
throw new RuntimeException("Failed to open: $filename");
}
// First row is the header:
$header = fgetcsv($handle);
while (($row = fgetcsv($handle)) !== false) {
yield array_combine($header, $row);
}
fclose($handle);
}
// Use it like this:
foreach (readCsvLineByLine(__DIR__ . '/large-data.csv') as $record) {
// Each $record is an associative array, e.g. ['id'=>'123', 'name'=>'Alice', …]
// Process $record without loading the entire file into memory.
}
Because fgetcsv() reads one line at a time and yield returns one row, PHP never loads the whole file at once.
When to Use Generators
- Fetching thousands of database rows:
yieldeach row instead offetchAll(). - Processing large log files or text files line by line.
- Any situation where you would otherwise build a huge array.
Generators make your PHP code run “lazy”: values are produced on demand. This keeps memory usage low and avoids slowdowns. Next time you need to handle big data in PHP, try a Generator function!
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