PHP
Summary - Class constants
Build an order class with status constants using const, :: and ::class.
Summary - Class constants
In this group you learned class constants:
const defines a class constant; no $ sign, immutable.- The
:: operator reaches constants from outside with ClassName::CONSTANT and from inside with self::CONSTANT. ::class returns the fully qualified class name as a string.- Constants are immutable; static properties can change.
- Great for configuration, status codes and enum-like structures.
Now you'll combine these in an Order class with status constants.
Exercise Order class with status constants
Define an Order class with const string PENDING = 'pending'; and const string SHIPPED = 'shipped';. Add a private string $status property and a public function __construct(string $status = self::PENDING) that assigns $this->status = $status. Add public function label(): string with if ($this->status === self::SHIPPED) { return 'Shipped'; } and a final return 'Pending'. Then create $order = new Order(Order::SHIPPED) and print echo $order->label() . "\n". (Expected output: Shipped)
Show example solution
:PENDING) { $this->status = $status; } public function label(): string { if ($this->status === self::SHIPPED) { return 'Shipped'; } return 'Pending'; } } then $order = new Order(Order::SHIPPED); echo $order->label() . "\n";
Example solution:
<?php
// Define an Order class
class Order {
const string PENDING = 'pending';
const string SHIPPED = 'shipped';
private string $status;
public function __construct(string $status = self::PENDING) {
$this->status = $status;
}
public function label(): string {
if ($this->status === self::SHIPPED) {
return 'Shipped';
}
return 'Pending';
}
}
$order = new Order(Order::SHIPPED);
echo $order->label() . "
";
Tips for class constants
In summary: use const for immutable values and static for mutable ones. Access constants with ::; self:: inside, ClassName:: outside.
Use constants for configuration, status codes and enum-like structures. This makes your code more readable and safe; it avoids the magic number and magic string problems.
In the next group you'll learn to define contracts between classes with interfaces.
Test yourself
-
Match the class constant concepts
- const
- Defines a class constant
- ::
- Operator to access constants
- ::class
- Gives the fully qualified name
- self::
- In-class access
-
For order status in an e-commerce app, what is the best choice?
- Statuses defined as class constants (const)
- A separate variable for each order
- Writing a new string in the database each time
- Storing it as a public property
Show answer
Statuses defined as class constants (const) — Correct. Order statuses are immutable values; a class constant is ideal.
Next lesson: Project: Quiz app
