PHP में FOR vs FOREACH Performance Comparison

PHP में for और foreach loops के performance characteristics और कब कौन सा उपयोग करें।

मूल अंतर

• for - Index-based, manual control, slightly faster for numeric arrays
• foreach - Iterator-based, cleaner syntax, copies array by default (PHP 7 तक)

Performance Test Code

<?php
$arr = range(1, 100000); // 100k elements

// Test 1: foreach by value (copies array in PHP < 7)
$start = microtime(true);
foreach ($arr as $v) { $v += 1; }
echo "foreach (value): " . (microtime(true) - $start) . "s\n";

// Test 2: foreach by reference (modifies original, no copy)
$start = microtime(true);
foreach ($arr as &$v) { $v += 1; }
echo "foreach (ref): " . (microtime(true) - $start) . "s\n";

// Test 3: for loop
$start = microtime(true);
for ($i = 0, $len = count($arr); $i < $len; $i++) {
    $arr[$i] += 1;
}
echo "for loop: " . (microtime(true) - $start) . "s\n";

// Test 4: foreach read-only (no modification)
$start = microtime(true);
foreach ($arr as $v) { /* read only */ }
echo "foreach (read): " . (microtime(true) - $start) . "s\n";

Typical Results (PHP 8.x, 100k elements)

PHP Version Differences

• PHP 5.x: foreach हमेशा array copy करता है → slow for large arrays
• PHP 7+: Copy-on-write optimization → read-only foreach fast
• PHP 8+: Further optimizations, JIT compilation benefits

कब क्या उपयोग करें

महत्वपूर्ण: Reference Cleanup

<?php
$arr = [1, 2, 3];

foreach ($arr as &$v) {
    $v *= 2;
}
unset($v); // महत्वपूर्ण! $v अभी भी last element को reference करता है

// बिना unset के:
$v = 999; // $arr[2] भी 999 हो जाता है!
print_r($arr); // [2, 4, 999] - Bug!

Modern PHP (8.1+) Alternatives

// array_map - functional, immutable
$doubled = array_map(fn($x) => $x * 2, $arr);

// array_walk - in-place modification
array_walk($arr, fn(&$v) => $v *= 2);

// Generator for memory efficiency
function processLargeArray(iterable $data) {
    foreach ($data as $item) {
        yield $item * 2;
    }
}

निष्कर्ष

अधिकांश मामलों में पठनीयता के लिए foreach उपयोग करें। Performance critical code में ही for या reference-based foreach पर विचार करें। Premature optimization से बचें।