Feat: Transformers can now return single values for a better DX (#12)

README.md

@@ -35,9 +35,7 @@ Now let's have a look on how simple it is:
 use Bentools\ETL\EtlExecutor;
 
 $etl = (new EtlExecutor())
-    ->transformWith(function (string $name) {
-        yield strtoupper($name);
-    });
+    ->transformWith(fn (string $name) => strtoupper($name));
 
 $singers = ['Bob Marley', 'Amy Winehouse'];
 $report = $etl->process($singers);
@@ -128,7 +126,9 @@ $etl = (new EtlExecutor())
 $etl->process('file:///tmp/cities.csv', $pdo);
 ```
 
-As you can see, you can use `EtlState.destination` to retrieve the second argument you passed yo `$etl->process()`.
+As you can see:
+- Your transformer can _yield_ values, in case 1 extracted item becomes several items to load
+- You can use `EtlState.destination` to retrieve the second argument you passed yo `$etl->process()`.
 
 The `EtlState` object contains all elements relative to the state of your ETL workflow being running.
 

src/EtlExecutor.php

@@ -118,7 +118,8 @@ private function extract(EtlState &$state): Generator
     private function transform(mixed $item, EtlState $state): array
     {
         try {
-            $items = [...$this->transformer->transform($item, $state)];
+            $transformed = $this->transformer->transform($item, $state);
+            $items = $transformed instanceof Generator ? [...$transformed] : [$transformed];
 
             return $this->dispatch(new TransformEvent($state, $items))->items;
         } catch (SkipRequest|StopRequest $e) {

src/Transformer/CallableTransformer.php

@@ -6,7 +6,6 @@
 
 use Bentools\ETL\EtlState;
 use Closure;
-use Generator;
 
 final readonly class CallableTransformer implements TransformerInterface
 {
@@ -15,10 +14,7 @@ public function __construct(
     ) {
     }
 
-    /**
-     * @return Generator<mixed>
-     */
-    public function transform(mixed $item, EtlState $state): Generator
+    public function transform(mixed $item, EtlState $state): mixed
     {
         return ($this->closure)($item, $state);
     }

src/Transformer/NullTransformer.php

@@ -5,12 +5,11 @@
 namespace Bentools\ETL\Transformer;
 
 use Bentools\ETL\EtlState;
-use Generator;
 
 final readonly class NullTransformer implements TransformerInterface
 {
-    public function transform(mixed $item, EtlState $state): Generator
+    public function transform(mixed $item, EtlState $state): mixed
     {
-        yield $item;
+        return $item;
     }
 }

src/Transformer/TransformerInterface.php

@@ -5,12 +5,8 @@
 namespace Bentools\ETL\Transformer;
 
 use Bentools\ETL\EtlState;
-use Generator;
 
 interface TransformerInterface
 {
-    /**
-     * @return Generator<mixed>
-     */
-    public function transform(mixed $item, EtlState $state): Generator;
+    public function transform(mixed $item, EtlState $state): mixed;
 }

tests/Unit/EtlExecutorTest.php

@@ -10,13 +10,13 @@
 use function expect;
 use function strtoupper;
 
-it('basically works', function () {
+it('basically works', function (callable $transformer) {
     $items = [];
 
     // Given
     $etl = (new EtlExecutor())
         ->extractFrom(fn () => yield from ['foo', 'bar'])
-        ->transformWith(fn (mixed $value) => yield strtoupper($value))
+        ->transformWith($transformer)
         ->loadInto(function (string $item) use (&$items) {
             $items[] = $item;
         })
@@ -31,4 +31,7 @@
         ->and($report->nbLoadedItems)->toBe(2)
         ->and($report->getDuration())->toBeBetween(0, 1)
     ;
+})->with(function () {
+    yield 'Return value' => fn (mixed $value) => strtoupper($value);
+    yield 'Generator' => fn (mixed $value) => yield strtoupper($value);
 });

tests/Unit/Transformer/NullTransformerTest.php

@@ -8,7 +8,6 @@
 use Bentools\ETL\Transformer\NullTransformer;
 
 use function expect;
-use function iterator_to_array;
 
 it('yields the value as-is', function () {
     // Given
@@ -19,5 +18,5 @@
     $transformedItems = $transformer->transform('foo', $state);
 
     // Then
-    expect(iterator_to_array($transformedItems))->toBe(['foo']);
+    expect($transformedItems)->toBe('foo');
 });