PHP Function Parameters and Arguments Explained

A function gets more useful when you can give it data to work with. The values it accepts are called parameters.

index.php

PHP

<?php
function greet(string $name): void
{
    echo "Hello, $name!\n";
}

greet("Asha");
greet("Ben");

Output

OUTPUT

1
2

Hello, Asha!
Hello, Ben!

Parameter vs argument

These two words are easy to mix up.

A parameter is the variable in the function definition: $name.
An argument is the value you pass when you call it: "Asha".

Think of a parameter as an empty seat and an argument as the person who sits in it.

More than one parameter

Separate them with commas. Arguments are matched by position.

index.php

PHP

<?php
function introduce(string $name, int $age, string $city): void
{
    echo "$name is $age years old and lives in $city.\n";
}

introduce("Ravi", 28, "Delhi");

Output

OUTPUT

Ravi is 28 years old and lives in Delhi.

If you swap the order, you swap the meaning: introduce(28, "Ravi", ...) would be wrong. PHP can help you catch it with types, and Named Arguments make it even safer.

Too few arguments

If you forget a required argument, PHP throws an error.

index.php

PHP

<?php
function add(int $a, int $b): int
{
    return $a + $b;
}

try {
    echo add(5);
} catch (ArgumentCountError $e) {
    echo $e->getMessage();
}

Output

OUTPUT

Too few arguments to function add(), 1 passed in /path/to/index.php on line 8 and exactly 2 expected

Too many arguments

Extra arguments to your own function are ignored, with no error.

index.php

PHP

<?php
function add(int $a, int $b): int
{
    return $a + $b;
}

echo add(1, 2, 3);

Output

OUTPUT

Arguments can be any expression

index.php

PHP

<?php
function double(int $n): int
{
    return $n * 2;
}

$base = 4;

echo double($base) . "\n";
echo double($base + 1) . "\n";
echo double(double(3));

Output

OUTPUT

1
2
3

8
10
12

Arrays and other types

A parameter can hold any type, including an array.

index.php

PHP

<?php
function listItems(array $items): void
{
    foreach ($items as $item) {
        echo "- $item\n";
    }
}

listItems(["tea", "coffee"]);

Output

OUTPUT

1
2

- tea
- coffee

lightbulb

Keep parameter lists short

More than three or four parameters is a sign that the function does too much, or that the values belong together in an array or an object.