Added withData method for immutable reusability

src/Valitron/Validator.php

@@ -1085,4 +1085,19 @@ class Validator
             }
         }
     }
+
+    /**
+     * Replace data on cloned instance
+     *
+     * @param  array $data
+     * @param  array $fields
+     * @return Valitron
+     */
+    public function withData($data, $fields = array())
+    {
+        $clone = clone $this;
+        $clone->reset();
+        $clone->_fields = !empty($fields) ? array_intersect_key($data, array_flip($fields)) : $data;
+        return $clone;
+    }
 }

tests/Valitron/ValidateTest.php

@@ -1156,6 +1156,19 @@ class ValidateTest extends BaseTestCase
         $v->rule('optional', 'address')->rule('email', 'address');        
         $this->assertTrue($v->validate());
     }
+
+    public function testWithData()
+    {
+        $v = new Validator(array());
+        $v->rule('required', 'name');
+        //validation failed, so must have errors
+        $this->assertFalse($v->validate());
+        $this->assertNotEmpty($v->errors());
+        //create copy with different data
+        $v2 = $v->withData(array('name' => 'Chester Tester'));
+        $this->assertTrue($v2->validate());
+        $this->assertEmpty($v2->errors());
+    }
 }
 
 function sampleFunctionCallback($field, $value, array $params) {