Initial work on making export of objects customizable

src/Exporter.php

@@ -36,6 +36,13 @@
 
 final readonly class Exporter
 {
+    private ?ObjectExporterChain $objectExporter;
+
+    public function __construct(?ObjectExporterChain $objectExporter = null)
+    {
+        $this->objectExporter = $objectExporter;
+    }
+
     /**
      * Exports a value as a string.
      *
@@ -337,6 +344,10 @@ private function exportObject(mixed $value, RecursionContext $processed, string
 
         $processed->add($value);
 
+        if ($this->objectExporter !== null && $this->objectExporter->handles($value)) {
+            return $this->objectExporter->export($value);
+        }
+
         $values = '';
         $array  = $this->toArray($value);
 

src/ObjectExporter.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/exporter.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Exporter;
+
+interface ObjectExporter
+{
+    public function handles(object $object): bool;
+
+    public function export(object $object): string;
+}

src/ObjectExporterChain.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/exporter.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Exporter;
+
+final class ObjectExporterChain implements ObjectExporter
+{
+    /**
+     * @psalm-var non-empty-list<ObjectExporter>
+     */
+    private array $exporter;
+
+    /**
+     * @psalm-param non-empty-list<ObjectExporter> $exporter
+     */
+    public function __construct(array $exporter)
+    {
+        $this->exporter = $exporter;
+    }
+
+    public function handles(object $object): bool
+    {
+        foreach ($this->exporter as $exporter) {
+            if ($exporter->handles($object)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * @throws ObjectNotSupportedException
+     */
+    public function export(object $object): string
+    {
+        foreach ($this->exporter as $exporter) {
+            if ($exporter->handles($object)) {
+                return $exporter->export($object);
+            }
+        }
+
+        throw new ObjectNotSupportedException;
+    }
+}

src/exception/Exception.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/exporter.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Exporter;
+
+use Throwable;
+
+interface Exception extends Throwable
+{
+}

src/exception/ObjectNotSupportedException.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/exporter.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Exporter;
+
+use RuntimeException;
+
+final class ObjectNotSupportedException extends RuntimeException implements Exception
+{
+}

tests/ExporterTest.php

@@ -26,12 +26,14 @@
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\RequiresPhpExtension;
 use PHPUnit\Framework\Attributes\Small;
+use PHPUnit\Framework\Attributes\UsesClass;
 use PHPUnit\Framework\TestCase;
 use SebastianBergmann\RecursionContext\Context;
 use SplObjectStorage;
 use stdClass;
 
 #[CoversClass(Exporter::class)]
+#[UsesClass(ObjectExporterChain::class)]
 #[Small]
 final class ExporterTest extends TestCase
 {
@@ -486,6 +488,27 @@ public function testShortenedRecursiveOccurredRecursion(): void
         $this->assertEquals('*RECURSION*', (new Exporter)->shortenedRecursiveExport($value, $context));
     }
 
+    public function testExportOfObjectsCanBeCustomized(): void
+    {
+        $objectExporter = $this->createStub(ObjectExporter::class);
+        $objectExporter->method('handles')->willReturn(true);
+        $objectExporter->method('export')->willReturn('custom object export');
+
+        $exporter = new Exporter(new ObjectExporterChain([$objectExporter]));
+
+        $this->assertSame(
+            <<<'EOT'
+Array &0 [
+    0 => custom object export,
+    1 => custom object export,
+]
+EOT
+            ,
+            $exporter->export([new stdClass, new stdClass]),
+        );
+
+    }
+
     private function trimNewline(string $string): string
     {
         return preg_replace('/[ ]*\n/', "\n", $string);

tests/ObjectExporterChainTest.php

@@ -0,0 +1,62 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/exporter.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Exporter;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Small;
+use PHPUnit\Framework\TestCase;
+use stdClass;
+
+#[CoversClass(ObjectExporterChain::class)]
+#[Small]
+final class ObjectExporterChainTest extends TestCase
+{
+    public function testCanBeQueriedWhetherChainedExporterHandlesAnObject(): void
+    {
+        $firstExporter = $this->createStub(ObjectExporter::class);
+        $firstExporter->method('handles')->willReturn(false);
+
+        $secondExporter = $this->createStub(ObjectExporter::class);
+        $secondExporter->method('handles')->willReturn(true);
+
+        $chain = new ObjectExporterChain([$firstExporter]);
+        $this->assertFalse($chain->handles(new stdClass));
+
+        $chain = new ObjectExporterChain([$firstExporter, $secondExporter]);
+        $this->assertTrue($chain->handles(new stdClass));
+    }
+
+    public function testDelegatesExportingToFirstExporterThatHandlesAnObject(): void
+    {
+        $firstExporter = $this->createStub(ObjectExporter::class);
+        $firstExporter->method('handles')->willReturn(false);
+        $firstExporter->method('export')->willThrowException(new ObjectNotSupportedException);
+
+        $secondExporter = $this->createStub(ObjectExporter::class);
+        $secondExporter->method('handles')->willReturn(true);
+        $secondExporter->method('export')->willReturn('string');
+
+        $chain = new ObjectExporterChain([$firstExporter, $secondExporter]);
+
+        $this->assertSame('string', $chain->export(new stdClass));
+    }
+
+    public function testCannotExportObjectWhenNoExporterHandlesIt(): void
+    {
+        $firstExporter = $this->createStub(ObjectExporter::class);
+        $firstExporter->method('handles')->willReturn(false);
+
+        $chain = new ObjectExporterChain([$firstExporter]);
+
+        $this->expectException(ObjectNotSupportedException::class);
+
+        $this->assertSame('string', $chain->export(new stdClass));
+    }
+}