How to specify parameters of PHP function? What types can they be?

The parameter passing methods of PHP functions include: passing by value, passing by reference and default value parameters. Parameter type checking of original and composite types is supported. In actual applications, passing by value will not affect the original value, while passing by reference will. Modify the original value, and the default value parameter provides a default value.

Parameter specification and type of PHP function

The parameters of the function in PHP can be specified as:

Passed by value ( Default)

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

Pass by reference

function increment(&$a) {
  $a++;
}

Default value

function greet($name = "World") {
  echo "Hello, $name!";
}

Parameter type

Parameter type can be:

• Primitive type: Integer, floating point number, string, Boolean value
• Composite Type: Array, object
• Empty: Indicates that any type of parameter can be accepted

Example

function formatDate(DateTime $date) {
  // 对 DateTime 对象操作
}

function avg(int $a, int $b): float {
  return ($a + $b) / 2;
}

Practical case

Pass by value and pass by reference

function doubleValue($value) {
  $value *= 2;
}

$x = 10;
doubleValue($x);  // $x 不会改变，因为按值传递
echo $x;  // 输出 10

function doubleValueByRef(&$value) {
  $value *= 2;
}

doubleValueByRef($x);  // $x 已修改，因为按引用传递
echo $x;  // 输出 20

Default value and type checking

function greeting($name = "World") {
  echo "Hello, $name!";
}

greeting();  // 显示 "Hello, World!"
greeting("Alice");  // 显示 "Hello, Alice!"

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