What are the restrictions on how parameters are passed to PHP functions?

PHP function parameter passing methods: pass by value (copy) and pass by reference (original variable); restriction: variables can only be passed by reference and must be assigned a value.

Parameter passing methods and restrictions of PHP functions

Parameter passing methods

There are two main ways to pass parameters in PHP:

• Pass-by-Value: The function copies the value of the parameter, and any changes to the parameter within the function None of the changes affect the original variables outside the function.
• Pass-by-Reference : The function receives a reference to the original variable, and changes to the parameters within the function will also be reflected in the original variable outside the function.

Restrictions

PHP has some restrictions on how function parameters are passed:

• Pass by reference Restrictions

  • You can only use variables as arguments passed by reference.
  • Parameters passed by reference must be assigned within the function, otherwise an error will occur.

Practical case

Pass by value

function sum(int $num1, int $num2) {
  $result = $num1 + $num2;
  return $result;
}

$a = 5;
$b = 10;

$result = sum($a, $b); // $result 为 15，$a 和 $b 不受影响

By reference Pass

function swap(int &$num1, int &$num2) {
  $temp = $num1;
  $num1 = $num2;
  $num2 = $temp;
}

$a = 5;
$b = 10;

swap($a, $b); // $a = 10，$b = 5

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