What are the parameters passing methods for PHP functions?

PHP function parameters can be passed by reference or by value. Passing by value does not modify the external variable, while passing by reference modifies the external variable directly, enabled using the & symbol. Passing by reference is often used to modify array elements and optimize performance.

Parameter passing method of PHP function

In PHP, function parameters can be passed by reference or by value. These two transfer methods determine whether modifications to parameters inside the function will affect variables outside the function.

Pass by value

Pass by value is PHP’s default parameter passing method. In this way, any modification of parameter values ​​inside the function will not affect variables outside the function. This is because PHP creates a copy of the parameter value when passing it.

function add_by_value($a, $b) {
  $a += $b;
}

$x = 10;
$y = 5;

add_by_value($x, $y);

echo $x; // 输出 10，因为 $x 的值没有被修改

Pass by reference

If you want to modify variables outside the function, you can use pass by reference. In pass-by-reference, modifications to parameters inside the function will be directly reflected in variables outside the function. This is because PHP creates a reference to the parameter when passing it, rather than a copy.

To enable reference passing, you need to add the & symbol before the function parameters.

function add_by_reference(&$a, &$b) {
  $a += $b;
}

$x = 10;
$y = 5;

add_by_reference($x, $y);

echo $x; // 输出 15，因为 $x 的值被修改了

Practical case

In actual development, reference passing is mainly used in the following scenarios:

• Modify array elements: When modifications are required Elements in an array can be passed by reference. For example, the following code modifies elements in an array by passing by reference:

function modify_array_element(&$array, $key, $value) {
  $array[$key] = $value;
}

$array = ['foo' => 'bar'];
modify_array_element($array, 'foo', 'new_value');
echo $array['foo']; // 输出 new_value

• Optimize performance: For large data structures, passing by value may cause an efficiency loss. Using pass-by-reference optimizes performance by avoiding unnecessary copies.

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