1. Constants using define():
- Definition: define(name, value, case_insensitive)
- Description: Creates a global constant with a fixed value.
define('PI', 3.14159);
// Accessing the constant:
echo PI; // Output: 3.14159
2. Class Constants using const keyword:
- Definition: const name = value; (within a class)
- Description: Creates a constant accessible only within the class and its instances.
class Circle {
const PI = 3.14159;
public function getArea($radius) {
return self::PI * $radius * $radius;
}
}
// Accessing the constant:
echo Circle::PI; // Output: 3.14159
3. Readonly Properties (PHP 8.1+):
- Definition: class MyClass { public readonly property $name = value; }
- Description: Declares a property that can only be set during object initialization.
class User {
public readonly string $id = '12345';
}
$user = new User();
$user->id = '98765'; // Error: Cannot modify readonly property
4. Getter Methods:
- Description: Create a method to access a value without directly exposing a mutable variable.
class Config {
private $apiKey = 'your_api_key';
public function getApiKey() {
return $this->apiKey;
}
}
$config = new Config();
$apiKey = $config->getApiKey();
echo $apiKey; // your_api_key
