PHP Functions

Functions are reusable blocks of code that perform a specific task. PHP supports named functions, anonymous functions, arrow functions, and more.

Declaring and Calling Functions

Use the function keyword. Parameters can have default values and type declarations.

Function Basics

<?php
// Basic function
function greet(string $name): string {
    return "Hello, $name!";
}
echo greet("Alice"); // Hello, Alice!

// Default parameter
function power(int $base, int $exp = 2): int {
    return $base ** $exp;
}
echo power(3);    // 9
echo power(3, 3); // 27

// Pass by reference
function addTen(int &$num): void {
    $num += 10;
}
$val = 5;
addTen($val);
echo $val; // 15

// Variadic function
function sum(int ...$nums): int {
    return array_sum($nums);
}
echo sum(1, 2, 3, 4, 5); // 15
?>

Anonymous Functions & Closures

Anonymous functions (closures) have no name and can be assigned to variables or passed as arguments. Use use to capture variables from the outer scope.

Anonymous Functions

<?php
// Anonymous function assigned to variable
$double = function(int $n): int {
    return $n * 2;
};
echo $double(5); // 10

// Closure capturing outer variable
$multiplier = 3;
$multiply = function(int $n) use ($multiplier): int {
    return $n * $multiplier;
};
echo $multiply(4); // 12

// Passing anonymous function as argument
$numbers = [3, 1, 4, 1, 5, 9];
usort($numbers, function($a, $b) { return $a - $b; });
print_r($numbers); // [1, 1, 3, 4, 5, 9]

// array_map with anonymous function
$squared = array_map(fn($n) => $n ** 2, [1, 2, 3, 4]);
print_r($squared); // [1, 4, 9, 16]
?>

Arrow Functions (PHP 7.4+)

Arrow functions use the fn keyword and automatically capture variables from the outer scope without needing use.

Arrow Functions

<?php
$tax = 0.2;

// Arrow function auto-captures $tax
$withTax = fn(float $price): float => $price * (1 + $tax);

echo $withTax(100); // 120

// Chaining with array functions
$prices = [10, 20, 30, 40];
$discounted = array_map(fn($p) => $p * 0.9, $prices);
$expensive  = array_filter($discounted, fn($p) => $p > 20);

print_r($expensive); // [27, 36]
?>

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PHP Functions

Declaring and Calling Functions

Anonymous Functions & Closures

Arrow Functions (PHP 7.4+)

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