Typed parameters
Learn to declare a parameter's type (int, string, array) and get an error on wrong types.
Type declaration
A type declaration states in the function signature which type a parameter accepts. The type is written before the parameter name.
Example: function add(int $a, int $b) { return $a + $b; }. Here int $a and int $b accept only integers. The call add(5, 3) works and returns 8; passing an incompatible type throws a TypeError.
int, string and array types
Common PHP parameter types are int (integer), string and array. The type is written before the parameter name.
Examples: function double(int $n) expects an integer; function printLabel(string $label) expects a string; function sum(array $items) expects an array. Passing the wrong type throws a TypeError, so mistakes are caught early at the call site.
Exercise Double a number
Define a function double with an int $n parameter. In the body write return $n * 2;. Then print the result with echo double(21) . "\n";.
Show example solution
Define function double(int $n) { ... }, put return $n * 2; in the body, then call with echo double(21) . "\n";.
Example solution:
<?php
// Define double and call it
function double(int $n) {
return $n * 2;
}
echo double(21) . "\n";Test yourself
-
Which one is a typed function?
- function add($a, $b) { ... }
- function add(a, b) { ... }
- function add(int, int) { ... }
- function add(int $a, int $b) { ... }
Show answer
function add(int $a, int $b) { ... } — Correct. int $a and int $b declare the parameter types.
-
Complete the type declaration
function printLabel(____) { echo $label; }Show answer
function printLabel(string $label) { echo $label; } -
Match type declarations
- int $n
- Integer parameter
- string $label
- String parameter
- array $items
- Array parameter