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title:
  - value: |
      Immutable read-only properties in PHP 8.1
created:
  - value: '2023-04-13T00:00:00+00:00'
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  - value: '2025-05-11T09:00:44+00:00'
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body:
  - value: |
      <p>Continuing with yesterday's data transfer object (DTO) example, something that can be done since PHP 8.1 is to make properties read-only:</p>

      <pre><code class="language-php">class AccountDetails {

        public function __construct(
        public readonly string $accountNumber,
        public readonly string $sortCode,
        ) {}

      }
      </code></pre>

      <p>This means the public properties can be read and used without the need for getter methods, but cannot be overridden - making the DTO immutable.</p>

      <p>Without <code>readonly</code>, a DTO can be created and the property values can be changed:</p>

      <pre><code class="language-php">$accountDetails = new AccountDetails('12345678', '00-00-00');
      $accountDetails-&gt;accountNumber = 'banana';
      </code></pre>

      <p>With <code>readonly</code> set, you'd get a fatal error instead:</p>

      <blockquote>
        <p>Fatal error: Uncaught Error: Cannot modify readonly property AccountDetails::$accountNumber in /home/opdavies/tmp/example.php:13</p>
      </blockquote>

              
    format: full_html
    processed: |
      <p>Continuing with yesterday's data transfer object (DTO) example, something that can be done since PHP 8.1 is to make properties read-only:</p>

      <pre><code class="language-php">class AccountDetails {

        public function __construct(
        public readonly string $accountNumber,
        public readonly string $sortCode,
        ) {}

      }
      </code></pre>

      <p>This means the public properties can be read and used without the need for getter methods, but cannot be overridden - making the DTO immutable.</p>

      <p>Without <code>readonly</code>, a DTO can be created and the property values can be changed:</p>

      <pre><code class="language-php">$accountDetails = new AccountDetails('12345678', '00-00-00');
      $accountDetails-&gt;accountNumber = 'banana';
      </code></pre>

      <p>With <code>readonly</code> set, you'd get a fatal error instead:</p>

      <blockquote>
        <p>Fatal error: Uncaught Error: Cannot modify readonly property AccountDetails::$accountNumber in /home/opdavies/tmp/example.php:13</p>
      </blockquote>

              
    summary: null
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