Callbacks, JSON & Exceptions

A callback is a function passed to another function. array_map(), usort(), and array_filter() use callbacks often.

Callbacks

A callback is a function passed to another function. array_map(), usort(), and array_filter() use callbacks often.

Real-life example: A callback is giving a friend your phone number and saying "call me when dinner is ready."

array_map and anonymous functions

<?php
$prices = [100, 200, 300];

$discounted = array_map(function ($p) {
  return $p * 0.9;
}, $prices);

print_r($discounted);

// Named callback
function double(int $n): int { return $n * 2; }
$nums = array_map("double", [1, 2, 3]);
?>

JSON — json_encode and json_decode

JSON is the standard data format for APIs. json_encode() turns PHP arrays into JSON strings. json_decode() parses JSON into arrays or objects.

Real-life example: JSON is a universal packing box — PHP, JavaScript, and mobile apps all understand the same label.

JSON encode/decode

<?php
$user = ["name" => "Asha", "courses" => ["PHP", "MySQL"]];

$json = json_encode($user);
echo $json;

$parsed = json_decode($json, true); // true = associative array
echo $parsed["name"];
?>

Exceptions

Use try { } catch (Exception $e) { } to handle errors gracefully. throw new Exception('message') signals failure.

Real-life example: Exceptions are fire alarms — normal work stops, you handle the problem, then continue safely.

try/catch/finally

<?php
function divide(int $a, int $b): float {
  if ($b === 0) {
    throw new InvalidArgumentException("Cannot divide by zero");
  }
  return $a / $b;
}

try {
  echo divide(10, 2);
  echo divide(10, 0);
} catch (InvalidArgumentException $e) {
  echo "Error: " . $e->getMessage();
} finally {
  echo "\nDone.";
}
?>