property.uninitializedReadonly

Code example

<?php declare(strict_types = 1);

class Foo
{
	private readonly int $assigned;

	private readonly int $unassigned;

	public function __construct()
	{
		$this->assigned = 1;
	}
}

Why is it reported?

A readonly property must be initialized exactly once during the object's construction. If a readonly property is not assigned in the constructor (or in a method configured as an additional constructor), it will remain uninitialized. Accessing an uninitialized readonly property at runtime throws an Error.

In the example above, $unassigned is declared as readonly but is never assigned in the constructor, so it will remain uninitialized.

This error is also reported when a readonly property is accessed before it has been assigned within the constructor, since the property is still in an uninitialized state at that point.

How to fix it

Assign the readonly property in the constructor:

 <?php declare(strict_types = 1);

 class Foo
 {
 	private readonly int $assigned;

 	private readonly int $unassigned;

 	public function __construct()
 	{
 		$this->assigned = 1;
+		$this->unassigned = 2;
 	}
 }

Or use constructor promotion to ensure the property is always initialized:

 <?php declare(strict_types = 1);

 class Foo
 {
-	private readonly int $assigned;
-
-	private readonly int $unassigned;
-
-	public function __construct()
-	{
-		$this->assigned = 1;
-	}
+	public function __construct(
+		private readonly int $assigned,
+		private readonly int $unassigned,
+	) {}
 }

If the property is initialized in a method other than __construct, configure that method as an additional constructor using the additionalConstructors configuration parameter.