PHP में array_merge vs Array Union (+) Operator का अंतर

PHP में दो arrays को merge करने के दो तरीके: array_merge() और + (union) operator। दोनों का व्यवहार अलग है।

Array Union Operator (+)

First array के keys को priority देता है। Duplicate keys पर first array का value रखता है।

<?php
$arr1 = ['p' => 150, 'q' => 100, 'r' => 120];
$arr2 = ['t' => 115, 'q' => 999, 'u' => 103]; // 'q' duplicate

$result = $arr1 + $arr2;

print_r($result);
/*
Array
(
    [p] => 150      // from arr1
    [q] => 100      // from arr1 (first wins!)
    [r] => 120      // from arr1
    [t] => 115      // from arr2
    [u] => 103      // from arr2
)
*/
// Note: arr2 का 'q' => 999 ignored हुआ

array_merge()

Later arrays के values से overwrite करता है। Numeric keys re-index होते हैं।

<?php
$arr1 = ['p' => 150, 'q' => 100, 'r' => 120];
$arr2 = ['t' => 115, 'q' => 999, 'u' => 103];

$result = array_merge($arr1, $arr2);

print_r($result);
/*
Array
(
    [p] => 150
    [q] => 999      // arr2 से overwrite हुआ!
    [r] => 120
    [t] => 115
    [u] => 103
)
*/

Numeric Keys के साथ व्यवहार

<?php
$arr1 = [0 => 'a', 1 => 'b'];
$arr2 = [0 => 'c', 1 => 'd'];

// Union (+) - keys preserve करता है
var_dump($arr1 + $arr2);
// array(2) { [0]=>'a' [1]=>'b' } - arr2 ignored!

// array_merge() - re-index करता है
var_dump(array_merge($arr1, $arr2));
// array(4) { [0]=>'a' [1]=>'b' [2]=>'c' [3]=>'d' }

तुलना तालिका

व्यावहारिक उदाहरण

<?php
// Config merging: defaults + user config
$defaults = [
    'host' => 'localhost',
    'port' => 3306,
    'debug' => false,
    'timeout' => 30
];

$userConfig = [
    'host' => 'db.example.com',
    'debug' => true
];

// Option 1: User config overrides defaults (array_merge)
$config = array_merge($defaults, $userConfig);
// Result: host=db.example.com, debug=true, port=3306, timeout=30

// Option 2: Defaults preserve, only add missing (union)
$config = $userConfig + $defaults;
// Result: host=db.example.com, debug=true, port=3306, timeout=30
// Same in this case because no numeric keys

// Multiple arrays merge
$config = array_merge($defaults, $envConfig, $userConfig, $runtimeConfig);
// Last one wins for duplicates

Recursive Merge (Deep Merge)

<?php
function arrayMergeRecursive(array ...$arrays): array {
    $result = [];
    
    foreach ($arrays as $array) {
        foreach ($array as $key => $value) {
            if (isset($result[$key]) && is_array($result[$key]) && is_array($value)) {
                $result[$key] = arrayMergeRecursive($result[$key], $value);
            } else {
                $result[$key] = $value;
            }
        }
    }
    
    return $result;
}

// या PHP 8.0+ में
$result = array_merge_recursive(...$arrays); // लेकिन यह numeric keys duplicate करता है!

सिफारिश

• Configuration merging: array_merge() (user overrides defaults)
• Preserving original keys: + operator
• Numeric indexed arrays combine:array_merge() (re-indexing wanted)
• Associative arrays combine (no overwrite):+ operator