Merge pull request #30 from pitchart/feature/length

Adds support for length

src/Reducer/Termination/Length.php

@@ -0,0 +1,25 @@
+<?php
+
+
+namespace Pitchart\Transformer\Reducer\Termination;
+
+
+use Pitchart\Transformer\Termination;
+
+class Length implements Termination
+{
+    public function init()
+    {
+        return 0;
+    }
+
+    public function step($result, $current)
+    {
+        return ++$result;
+    }
+
+    public function complete($result)
+    {
+        return $result;
+    }
+}

src/Transducer/transducers.php

@@ -629,3 +629,8 @@ function to_operation(string $operator)
 {
     return new Reducer\Termination\Operation($operator);
 }
+
+function length()
+{
+    return new Reducer\Termination\Length();
+}

src/Transformer.php

@@ -445,6 +445,14 @@ public function concat()
         return $this->terminate(t\to_operation('.'));
     }
 
+    /**
+     * @return string
+     */
+    public function length()
+    {
+        return $this->terminate(t\length());
+    }
+
     /**
      * Processes transducing with a Termination
      *

tests/Reducer/Termination/LengthTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Pitchart\Transformer\Tests\Reducer\Termination;
+
+use Pitchart\Transformer\Reducer;
+use Pitchart\Transformer\Reducer\Termination\Length;
+use PHPUnit\Framework\TestCase;
+use Pitchart\Transformer\Termination;
+use function Pitchart\Transformer\transform;
+
+class LengthTest extends TestCase
+{
+    public function test_is_a_reducer()
+    {
+        $length = new Length;
+        self::assertInstanceOf(Reducer::class, $length);
+    }
+
+    public function test_is_a_termination()
+    {
+        $length = new Length;
+        self::assertInstanceOf(Termination::class, $length);
+    }
+
+    public function test_is_zero_if_collection_is_empty()
+    {
+        $length = transform([])->length();
+
+        $this->assertEquals(0, $length);
+    }
+
+    public function test_returns_collection_size_for_not_empty_collections()
+    {
+        $length = transform([1, 2, 3, 4])->length();
+
+        $this->assertEquals(4, $length);
+    }
+}