From e416da6aab8c027c0046a2d628e892c982a195de Mon Sep 17 00:00:00 2001
From: Oliver Davies <oliver@oliverdavies.uk>
Date: Thu, 13 Apr 2023 23:50:06 +0100
Subject: [PATCH] daily-email: add 2023-04-13

---
 src/content/daily-email/2023-04-13.md | 35 +++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 src/content/daily-email/2023-04-13.md

diff --git a/src/content/daily-email/2023-04-13.md b/src/content/daily-email/2023-04-13.md
new file mode 100644
index 00000000..f4e01db6
--- /dev/null
+++ b/src/content/daily-email/2023-04-13.md
@@ -0,0 +1,35 @@
+---
+title: >
+  Immutable read-only properties in PHP 8.1
+pubDate: 2023-04-13
+permalink: >
+  archive/2023/04/13/immutable-read-only-properties-in-php-8-1
+tags:
+  - php
+---
+
+Continuing with yesterday's data transfer object (DTO) example, something that can be done since PHP 8.1 is to make properties read-only:
+
+```php
+class AccountDetails {
+
+  public function __construct(
+    public readonly string $accountNumber,
+    public readonly string $sortCode,
+  ) {}
+
+}
+```
+
+This means the public properties can be read and used without the need for getter methods, but cannot be overridden - making the DTO immutable.
+
+Without `readonly`, a DTO can be created and the property values can be changed:
+
+```php
+$accountDetails = new AccountDetails('12345678', '00-00-00');
+$accountDetails->accountNumber = 'banana';
+```
+
+With `readonly` set, you'd get a fatal error instead:
+
+> Fatal error: Uncaught Error: Cannot modify readonly property AccountDetails::$accountNumber in /home/opdavies/tmp/example.php:13