Ignore readonly properties

fixtures/f014/ReadonlyObjectProperty.php

@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace DeepCopy\f014;
+
+class ReadonlyObjectProperty
+{
+    public readonly ReadonlyScalarProperty $foo;
+
+    public function __construct()
+    {
+        $this->foo = new ReadonlyScalarProperty();
+    }
+}

fixtures/f014/ReadonlyScalarProperty.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types=1);
+
+namespace DeepCopy\f014;
+
+class ReadonlyScalarProperty
+{
+    public readonly string $foo;
+    public readonly int $bar;
+    public readonly array $baz;
+
+    public function __construct()
+    {
+        $this->foo = 'foo';
+        $this->bar = 1;
+        $this->baz = [];
+    }
+}

src/DeepCopy/DeepCopy.php

@@ -224,6 +224,11 @@ private function copyObjectProperty($object, ReflectionProperty $property)
             return;
         }
 
+        // Ignore readonly properties
+        if (method_exists($property, 'isReadOnly') && $property->isReadOnly()) {
+            return;
+        }
+
         // Apply the filters
         foreach ($this->filters as $item) {
             /** @var Matcher $matcher */

tests/DeepCopyTest/DeepCopyTest.php

@@ -21,6 +21,7 @@
 use DeepCopy\f011;
 use DeepCopy\f012\Suit;
 use DeepCopy\f013;
+use DeepCopy\f014;
 use DeepCopy\Filter\ChainableFilter;
 use DeepCopy\Filter\Doctrine\DoctrineProxyFilter;
 use DeepCopy\Filter\KeepFilter;
@@ -542,6 +543,23 @@ public function test_it_can_copy_property_after_applying_doctrine_proxy_filter_w
         $this->assertNotEquals($copy->getFoo(), $object->getFoo());
     }
 
+    /**
+     * @requires PHP 8.1
+     */
+    public function test_it_can_copy_object_with_readonly_property()
+    {
+        $scalarProperties = new f014\ReadonlyScalarProperty();
+        $objectProperties = new f014\ReadonlyObjectProperty();
+
+        $deepCopy = new DeepCopy();
+
+        $scalarPropertiesCopy = $deepCopy->copy($scalarProperties);
+        $objectPropertiesCopy = $deepCopy->copy($objectProperties);
+
+        $this->assertEqualButNotSame($scalarProperties, $scalarPropertiesCopy);
+        $this->assertEqualButNotSame($objectProperties, $objectPropertiesCopy);
+    }
+
     private function assertEqualButNotSame($expected, $val)
     {
         $this->assertEquals($expected, $val);