PHP Iterables

Iterable Interface & Generators (iterable, yield)

The iterable pseudo-type accepts any array or object implementing the Traversable interface (such as ArrayIterator or Generator). Generators provide a simple, memory-efficient way to iterate over large datasets without building arrays in memory using the yield keyword.

Generators vs Standard Arrays

Generator Memory Flow

flowchart TD
    A["foreach (readLargeFile() as $line)"] --> B["Generator Called"]
    B --> C["Reads 1 Line from File"]
    C --> D["yield $line (Pausable Execution)"]
    D --> E["Loop Processes Single Line"]
    E -->|Fetch Next| B

Practical Code Example

<?php
declare(strict_types=1);

// Generator Function yielding numbers lazily
function rangeGenerator(int $start, int $end): Generator
{
    for ($i = $start; $i <= $end; $i++) {
        // yield pauses function execution and returns single value
        yield $i;
    }
}

// Function accepting 'iterable' pseudo-type (Accepts both arrays & generators!)
function processCollection(iterable $items): void
{
    $sum = 0;
    foreach ($items as $item) {
        $sum += $item;
    }
    echo "Total Collection Sum: $sum
";
}

// Processing array vs generator seamlessly
$arrayCollection = [10, 20, 30];
$generatorCollection = rangeGenerator(1, 100);

processCollection($arrayCollection);
processCollection($generatorCollection);

echo "Memory Usage with Generator: " . round(memory_get_usage() / 1024, 2) . " KB
";

Best Practices

• Use iterable Type Hints for Flexible Methods: Type-hint iterable when a method needs to loop over data regardless of whether it receives an array or generator.
• Use Generators for Reading Massive Files & Logs: Use yield fgets($handle) when parsing huge log files to maintain minimal RAM usage.
• Keep Generators Single-Pass: Remember that generators cannot be rewound or accessed by index like standard arrays.

Self-Check Challenge

Write a generator function evenNumbers(int $max): Generator that uses yield to return all even numbers up to $max!