🐘 PHP Lesson 04 — Functions

1. Function Declaration

<?php

// Basic function
function greet($name) {
    return "Hello, $name!";
}

echo greet("Ko Min");   // "Hello, Ko Min!"
echo greet("Ma Aye");   // "Hello, Ma Aye!"

// Multiple parameters
function add($a, $b) {
    return $a + $b;
}
echo add(3, 4);   // 7

// No return = null
function sayHi() {
    echo "Hi!";
}

?>

2. Default Parameters

<?php

function greet($name = "Guest", $greeting = "Hello") {
    return "$greeting, $name!";
}

greet();                        // "Hello, Guest!"
greet("Ko Min");               // "Hello, Ko Min!"
greet("Ko Min", "Mingalaba");  // "Mingalaba, Ko Min!"

// ⚠️ Default params ကို ​နောက်မှ ထည့်ပါ
function bad($a = 1, $b) {}  // ❌ Error
function good($a, $b = 1) {} // ✅ OK

?>

3. Type Declarations (PHP 7+)

<?php

// Parameter type + return type
function add(int $a, int $b): int {
    return $a + $b;
}

function greet(string $name): string {
    return "Hello, $name";
}

function calculate(float $price, int $qty): float {
    return $price * $qty;
}

// Nullable type
function findUser(int $id): ?string {
    // returns string or null
    return $id === 1 ? "Ko Min" : null;
}

// void — no return value
function logMessage(string $msg): void {
    echo $msg;
}

?>

4. Variable Scope

<?php

$globalVar = "I'm global";

function myFunc() {
    // PHP မှာ global variable ကို function ထဲ တိုက်ရိုက် မဝင်ရဘူး!
    echo $globalVar;   // ❌ Error/undefined

    // global keyword သုံးရတယ်
    global $globalVar;
    echo $globalVar;   // ✅ "I'm global"
}

// Static variable — function call မှ တိုင်း မ reset
function counter() {
    static $count = 0;
    $count++;
    echo $count;
}
counter();  // 1
counter();  // 2
counter();  // 3

?>

5. Useful Built-in Functions

6. Anonymous Functions & Closures

<?php

// Anonymous function
$greet = function($name) {
    return "Hello, $name!";
};
echo $greet("Min");   // Hello, Min!

// Arrow function (PHP 7.4+)
$double = fn($n) => $n * 2;
echo $double(5);    // 10

// Used with array_map, array_filter
$numbers = [1, 2, 3, 4, 5];

$doubled = array_map(fn($n) => $n * 2, $numbers);
// [2, 4, 6, 8, 10]

$evens = array_filter($numbers, fn($n) => $n % 2 === 0);
// [2, 4]

// Closure use — bring outer variable in
$prefix = "Hello";
$greet2 = function($name) use ($prefix) {
    return "$prefix, $name!";
};

?>