diff --git a/spec/Check/CountCheckSpec.php b/spec/Check/CountCheckSpec.php
index 2dc068a..dd36f12 100644
--- a/spec/Check/CountCheckSpec.php
+++ b/spec/Check/CountCheckSpec.php
@@ -27,20 +27,20 @@ function it_implements_type_interface(TypeInterface $child)
     function it_returns_a_result_on_invalid_child_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(false);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 1);
 
-        $this->check([])->shouldHaveType(ResultInterface::class);
+        $this->check('', [])->shouldHaveType(ResultInterface::class);
     }
 
     function it_returns_a_result_on_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(true);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 1);
 
-        $this->check([3])->shouldHaveType(ResultInterface::class);
+        $this->check('', [3])->shouldHaveType(ResultInterface::class);
     }
 }
diff --git a/spec/Check/NumericRangeCheckSpec.php b/spec/Check/NumericRangeCheckSpec.php
index 25f72f1..ff38e28 100644
--- a/spec/Check/NumericRangeCheckSpec.php
+++ b/spec/Check/NumericRangeCheckSpec.php
@@ -28,20 +28,20 @@ function it_implements_type_interface(TypeInterface $child)
     function it_returns_a_result_on_invalid_child_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(false);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 0, 1);
 
-        $this->check(Argument::any())->shouldHaveType(ResultInterface::class);
+        $this->check('', Argument::any())->shouldHaveType(ResultInterface::class);
     }
 
     function it_returns_a_result_on_check(TypeInterface $child, ResultInterface $result)
     {
         $result->isValid()->willReturn(true);
-        $child->check(Argument::any())->willReturn($result);
+        $child->check('', Argument::any())->willReturn($result);
 
         $this->beConstructedWith($child, 0, 1);
 
-        $this->check(0)->shouldHaveType(ResultInterface::class);
+        $this->check('', 0)->shouldHaveType(ResultInterface::class);
     }
 }
diff --git a/spec/CheckerSpec.php b/spec/CheckerSpec.php
index 73b3340..548ec51 100644
--- a/spec/CheckerSpec.php
+++ b/spec/CheckerSpec.php
@@ -14,14 +14,15 @@ function it_is_initializable()
         $this->shouldHaveType(Checker::class);
     }
 
-    function it_accepts_a_type_and_an_array_as_parameter_for_fulfills(TypeInterface $type)
+    function it_accepts_a_type_and_an_array_as_parameter_for_fulfills(TypeInterface $type, ResultInterface $result)
     {
+        $type->check('', [])->willReturn($result);
         $this->fulfills([], $type);
     }
 
     function it_returns_the_result_of_the_type_in_fulfills(TypeInterface $type, ResultInterface $result)
     {
-        $type->check([])->willReturn($result);
+        $type->check('', [])->willReturn($result);
         $this->fulfills([], $type)->shouldBe($result);
     }
 }
diff --git a/spec/ResultSpec.php b/spec/ResultSpec.php
index d56c5ab..5817098 100644
--- a/spec/ResultSpec.php
+++ b/spec/ResultSpec.php
@@ -28,7 +28,7 @@ function it_will_return_is_invalid_if_it_was_set_in_constructor()
 
     function it_will_return_an_empty_array_if_no_error_list_is_given()
     {
-        $this->beConstructedWith(true);
+        $this->beConstructedWith(true, []);
         $this->getErrors()->shouldHaveCount(0);
     }
 }
diff --git a/spec/Type/AnyTypeSpec.php b/spec/Type/AnyTypeSpec.php
index a6d7327..422935d 100644
--- a/spec/Type/AnyTypeSpec.php
+++ b/spec/Type/AnyTypeSpec.php
@@ -15,25 +15,25 @@ function it_is_initializable()
 
     function it_should_return_valid_for_null()
     {
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 
     function it_should_return_empty_errors_for_null()
     {
-        $this->check(null)->getErrors()->shouldHaveCount(0);
+        $this->check('', null)->getErrors()->shouldHaveCount(0);
     }
 
     function it_should_return_valid_for_all_values()
     {
-        $this->check(true)->isValid()->shouldBe(true);
-        $this->check("foo")->isValid()->shouldBe(true);
-        $this->check(13)->isValid()->shouldBe(true);
+        $this->check('', true)->isValid()->shouldBe(true);
+        $this->check('', "foo")->isValid()->shouldBe(true);
+        $this->check('', 13)->isValid()->shouldBe(true);
     }
 
     function it_should_return_empty_errors_for_all_values()
     {
-        $this->check(true)->getErrors()->shouldHaveCount(0);
-        $this->check("foo")->getErrors()->shouldHaveCount(0);
-        $this->check(13)->getErrors()->shouldHaveCount(0);
+        $this->check('', true)->getErrors()->shouldHaveCount(0);
+        $this->check('', "foo")->getErrors()->shouldHaveCount(0);
+        $this->check('', 13)->getErrors()->shouldHaveCount(0);
     }
 }
diff --git a/spec/Type/BoolTypeSpec.php b/spec/Type/BoolTypeSpec.php
index 30fc953..6a81345 100644
--- a/spec/Type/BoolTypeSpec.php
+++ b/spec/Type/BoolTypeSpec.php
@@ -15,16 +15,16 @@ function it_is_initializable()
 
     function it_should_return_valid_for_bool()
     {
-        $this->check(true)->isValid()->shouldBe(true);
-        $this->check(false)->isValid()->shouldBe(true);
+        $this->check('', true)->isValid()->shouldBe(true);
+        $this->check('', false)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1)->isValid()->shouldBe(false);
-        $this->check(1.0)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1)->isValid()->shouldBe(false);
+        $this->check('', 1.0)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/DatetimeTypeSpec.php b/spec/Type/DatetimeTypeSpec.php
index 177c5b8..b54efd7 100644
--- a/spec/Type/DatetimeTypeSpec.php
+++ b/spec/Type/DatetimeTypeSpec.php
@@ -18,18 +18,18 @@ function it_should_return_valid_for_correct_values()
     {
         $this->beConstructedWith('d-m-Y h:m:s', 'Europe/Berlin');
 
-        $this->check('12-12-2012 12:12:10')->isValid()->shouldBe(true);
+        $this->check('', '12-12-2012 12:12:10')->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
         $this->beConstructedWith('d-m-Y h:m:s', 'Europe/Berlin');
 
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check('foo')->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1.234)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 'foo')->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1.234)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/EnumTypeSpec.php b/spec/Type/EnumTypeSpec.php
index 73e7436..36cc405 100644
--- a/spec/Type/EnumTypeSpec.php
+++ b/spec/Type/EnumTypeSpec.php
@@ -18,18 +18,18 @@ function it_is_valid_for_all_allowed_values()
     {
         $this->beConstructedWith(['test', 1, null]);
 
-        $this->check('test')->isValid()->shouldBe(true);
-        $this->check(1)->isValid()->shouldBe(true);
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', 'test')->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 
     function it_is_invalid_for_not_allowed_values()
     {
         $this->beConstructedWith(['test', 1, null]);
-        
-        $this->check('array')->isValid()->shouldBe(false);
-        $this->check(100)->isValid()->shouldBe(false);
-        $this->check(1.5)->isValid()->shouldBe(false);
-        $this->check(['test'])->isValid()->shouldBe(false);
+
+        $this->check('', 'array')->isValid()->shouldBe(false);
+        $this->check('', 100)->isValid()->shouldBe(false);
+        $this->check('', 1.5)->isValid()->shouldBe(false);
+        $this->check('', ['test'])->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/ExactValueTypeSpec.php b/spec/Type/ExactValueTypeSpec.php
index f88dc8c..e6ebeae 100644
--- a/spec/Type/ExactValueTypeSpec.php
+++ b/spec/Type/ExactValueTypeSpec.php
@@ -17,6 +17,6 @@ function it_is_initializable()
     function it_is_valid_for_null_if_null_is_the_value()
     {
         $this->beConstructedWith(null);
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 }
diff --git a/spec/Type/FloatTypeSpec.php b/spec/Type/FloatTypeSpec.php
index 48e6dd1..2df6598 100644
--- a/spec/Type/FloatTypeSpec.php
+++ b/spec/Type/FloatTypeSpec.php
@@ -14,19 +14,19 @@ function it_is_initializable()
 
     function it_should_return_valid_for_floats()
     {
-        $this->check(0.0)->isValid()->shouldBe(true);
-        $this->check(1.1)->isValid()->shouldBe(true);
-        $this->check(2.0)->isValid()->shouldBe(true);
-        $this->check(-144.2)->isValid()->shouldBe(true);
+        $this->check('', 0.0)->isValid()->shouldBe(true);
+        $this->check('', 1.1)->isValid()->shouldBe(true);
+        $this->check('', 2.0)->isValid()->shouldBe(true);
+        $this->check('', -144.2)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/IntTypeSpec.php b/spec/Type/IntTypeSpec.php
index cb8eaf1..c710003 100644
--- a/spec/Type/IntTypeSpec.php
+++ b/spec/Type/IntTypeSpec.php
@@ -15,19 +15,19 @@ function it_is_initializable()
 
     function it_should_return_valid_for_integers()
     {
-        $this->check(0)->isValid()->shouldBe(true);
-        $this->check(1)->isValid()->shouldBe(true);
-        $this->check(20)->isValid()->shouldBe(true);
-        $this->check(-144)->isValid()->shouldBe(true);
+        $this->check('', 0)->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', 20)->isValid()->shouldBe(true);
+        $this->check('', -144)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(1.234)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', 1.234)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/NullableTypeSpec.php b/spec/Type/NullableTypeSpec.php
index 13bc912..0d68924 100644
--- a/spec/Type/NullableTypeSpec.php
+++ b/spec/Type/NullableTypeSpec.php
@@ -17,12 +17,12 @@ function it_is_initializable(TypeInterface $childType)
 
     function it_should_return_valid_for_null(TypeInterface $childType) {
         $this->beConstructedWith($childType);
-        $this->check(null)->isValid()->shouldBe(true);
+        $this->check('', null)->isValid()->shouldBe(true);
     }
 
     function it_should_return_the_value_from_the_child(TypeInterface $childType) {
         $this->beConstructedWith($childType);
-        $childType->check(false)->willReturn(new Result(false, []));
-        $this->check(false)->isValid()->shouldBe(false);
+        $childType->check('', false)->willReturn(new Result(false, []));
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/NumericTypeSpec.php b/spec/Type/NumericTypeSpec.php
index 8cb7af4..b3cfc29 100644
--- a/spec/Type/NumericTypeSpec.php
+++ b/spec/Type/NumericTypeSpec.php
@@ -15,26 +15,26 @@ function it_is_initializable()
 
     function it_should_return_valid_for_integers()
     {
-        $this->check(0)->isValid()->shouldBe(true);
-        $this->check(1)->isValid()->shouldBe(true);
-        $this->check(20)->isValid()->shouldBe(true);
-        $this->check(-144)->isValid()->shouldBe(true);
+        $this->check('', 0)->isValid()->shouldBe(true);
+        $this->check('', 1)->isValid()->shouldBe(true);
+        $this->check('', 20)->isValid()->shouldBe(true);
+        $this->check('', -144)->isValid()->shouldBe(true);
     }
 
     function it_should_return_valid_for_floats()
     {
-        $this->check(0.0)->isValid()->shouldBe(true);
-        $this->check(1.1235)->isValid()->shouldBe(true);
-        $this->check(-0.00001)->isValid()->shouldBe(true);
-        $this->check(-144.12313131313)->isValid()->shouldBe(true);
+        $this->check('', 0.0)->isValid()->shouldBe(true);
+        $this->check('', 1.1235)->isValid()->shouldBe(true);
+        $this->check('', -0.00001)->isValid()->shouldBe(true);
+        $this->check('', -144.12313131313)->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check("foo")->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
-        $this->check(false)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', "foo")->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/OptionalTypeSpec.php b/spec/Type/OptionalTypeSpec.php
index 5e3f6a8..61f4a38 100644
--- a/spec/Type/OptionalTypeSpec.php
+++ b/spec/Type/OptionalTypeSpec.php
@@ -17,7 +17,7 @@ function it_is_initializable(TypeInterface $childType)
 
     function it_should_return_the_value_from_the_child(TypeInterface $childType) {
         $this->beConstructedWith($childType);
-        $childType->check(false)->willReturn(new Result(false, []));
-        $this->check(false)->isValid()->shouldBe(false);
+        $childType->check('', false)->willReturn(new Result(false, []));
+        $this->check('', false)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/RegexTypeSpec.php b/spec/Type/RegexTypeSpec.php
index e2ad031..904ee25 100644
--- a/spec/Type/RegexTypeSpec.php
+++ b/spec/Type/RegexTypeSpec.php
@@ -19,24 +19,24 @@ function it_should_return_valid_for_matching_strings()
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check('definitive')->isValid()->shouldBe(true);
+        $this->check('', 'definitive')->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_not_matching_strings()
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check('developers')->isValid()->shouldBe(false);
+        $this->check('', 'developers')->isValid()->shouldBe(false);
     }
 
     function it_should_return_invalid_for_others()
     {
         $this->beConstructedWith('/^def/');
 
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check(12.3)->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(-1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 12.3)->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', -1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
     }
 }
diff --git a/spec/Type/StringTypeSpec.php b/spec/Type/StringTypeSpec.php
index 5bb35d6..f514c5f 100644
--- a/spec/Type/StringTypeSpec.php
+++ b/spec/Type/StringTypeSpec.php
@@ -15,17 +15,17 @@ function it_is_initializable()
 
     function it_should_return_valid_for_strings()
     {
-        $this->check("")->isValid()->shouldBe(true);
-        $this->check("fooo")->isValid()->shouldBe(true);
-        $this->check('adadsad asd a')->isValid()->shouldBe(true);
+        $this->check('', '')->isValid()->shouldBe(true);
+        $this->check('', 'fooo')->isValid()->shouldBe(true);
+        $this->check('', 'adadsad asd a')->isValid()->shouldBe(true);
     }
 
     function it_should_return_invalid_for_others()
     {
-        $this->check(null)->isValid()->shouldBe(false);
-        $this->check(12.3)->isValid()->shouldBe(false);
-        $this->check([])->isValid()->shouldBe(false);
-        $this->check(-1)->isValid()->shouldBe(false);
-        $this->check(true)->isValid()->shouldBe(false);
+        $this->check('', null)->isValid()->shouldBe(false);
+        $this->check('', 12.3)->isValid()->shouldBe(false);
+        $this->check('', [])->isValid()->shouldBe(false);
+        $this->check('', -1)->isValid()->shouldBe(false);
+        $this->check('', true)->isValid()->shouldBe(false);
     }
 }
diff --git a/src/Check/CountCheck.php b/src/Check/CountCheck.php
index 72d283e..6f09a2d 100644
--- a/src/Check/CountCheck.php
+++ b/src/Check/CountCheck.php
@@ -3,13 +3,11 @@
 namespace Cubicl\StructureCheck\Check;
 
 use Countable;
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class CountCheck
- * @package Cubicl\StructureCheck\Check
- */
 class CountCheck implements TypeInterface
 {
     /**
@@ -32,43 +30,32 @@ class CountCheck implements TypeInterface
      */
     private $count;
 
-    /**
-     * CountCheck constructor.
-     *
-     * @param TypeInterface $child
-     * @param int $count
-     */
-    public function __construct(TypeInterface $child, $count)
+    public function __construct(TypeInterface $child, int $count)
     {
         $this->child = $child;
         $this->count = $count;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        $result = $this->child->check($value);
+        $result = $this->child->check($key, $value);
 
         if (!$result->isValid()) {
             return $result;
         }
 
         if (!$value instanceof Countable) {
-            return new Result(
-                false,
-                [sprintf(self::$countableErrorMessage, json_encode($value))]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$countableErrorMessage, json_encode($value)))
+            ]);
         }
 
         if (count($value) !== $this->count) {
-            return new Result(
-                false,
-                [sprintf(self::$countErrorMessage, json_encode($value), $this->count)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$countErrorMessage, json_encode($value), $this->count))
+            ]);
         }
 
-        return new Result(true);
+        return Result::valid();
     }
 }
diff --git a/src/Check/NumericRangeCheck.php b/src/Check/NumericRangeCheck.php
index 414c2d9..a23a718 100644
--- a/src/Check/NumericRangeCheck.php
+++ b/src/Check/NumericRangeCheck.php
@@ -2,13 +2,11 @@
 
 namespace Cubicl\StructureCheck\Check;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class NumericRangeCheck
- * @package Cubicl\StructureCheck\Check
- */
 class NumericRangeCheck implements TypeInterface
 {
     /**
@@ -36,43 +34,33 @@ class NumericRangeCheck implements TypeInterface
      */
     private $upperBound;
 
-    /**
-     * @param TypeInterface $child
-     * @param int $upperBound
-     * @param int $lowerBound
-     */
-    public function __construct(TypeInterface $child, $upperBound, $lowerBound)
+    public function __construct(TypeInterface $child, int $upperBound, int $lowerBound)
     {
         $this->child = $child;
         $this->upperBound = $upperBound;
         $this->lowerBound = $lowerBound;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        $result = $this->child->check($value);
+        $result = $this->child->check($key, $value);
 
         if (!$result->isValid()) {
            return $result;
         }
 
         if ($this->lowerBound > $value) {
-            return new Result(
-                false,
-                [sprintf(self::$lowerBoundErrorMessage, $this->lowerBound, $value)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$lowerBoundErrorMessage, $this->lowerBound, $value))
+            ]);
         }
 
         if ($this->upperBound < $value) {
-            return new Result(
-                false,
-                [sprintf(self::$upperBoundErrorMessage, $this->upperBound, $value)]
-            );
+            return Result::invalid([
+                new Error($key, sprintf(self::$upperBoundErrorMessage, $this->lowerBound, $value))
+            ]);
         }
 
-        return new Result(true);
+        return Result::valid();
     }
 }
diff --git a/src/Checker.php b/src/Checker.php
index b7097a0..861a490 100644
--- a/src/Checker.php
+++ b/src/Checker.php
@@ -4,19 +4,13 @@
 
 use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Class Checker
- * @package Cubicl\StructureCheck
- */
 class Checker implements CheckerInterface
 {
-
     /**
      * @inheritdoc
      */
-    public function fulfills($element, TypeInterface $requirement)
+    public function fulfills($element, TypeInterface $requirement): ResultInterface
     {
-        return $requirement->check($element);
+        return $requirement->check('', $element);
     }
-
-}
\ No newline at end of file
+}
diff --git a/src/CheckerInterface.php b/src/CheckerInterface.php
index af764bc..1cc8ef3 100644
--- a/src/CheckerInterface.php
+++ b/src/CheckerInterface.php
@@ -4,18 +4,13 @@
 
 use Cubicl\StructureCheck\Type\TypeInterface;
 
-/**
- * Interface CheckerInterface
- * @package Cubicl\StructureCheck
- */
 interface CheckerInterface
 {
-
     /**
      * @param mixed $element the element which should be tested
      * @param TypeInterface $requirement
      *
      * @return ResultInterface
      */
-    public function fulfills($element, TypeInterface $requirement);
-}
\ No newline at end of file
+    public function fulfills($element, TypeInterface $requirement): ResultInterface;
+}
diff --git a/src/Error.php b/src/Error.php
new file mode 100644
index 0000000..d21a104
--- /dev/null
+++ b/src/Error.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Cubicl\StructureCheck;
+
+class Error implements ErrorInterface
+{
+    private $key;
+
+    private $message;
+
+    public function __construct(string $key, string $message)
+    {
+        $this->key = $key;
+        $this->message = $message;
+    }
+
+    public function getKey(): string
+    {
+        return $this->key;
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+}
diff --git a/src/ErrorInterface.php b/src/ErrorInterface.php
new file mode 100644
index 0000000..ffd6246
--- /dev/null
+++ b/src/ErrorInterface.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Cubicl\StructureCheck;
+
+interface ErrorInterface
+{
+    public function getKey(): string;
+
+    public function getMessage(): string;
+}
diff --git a/src/Result.php b/src/Result.php
index bf6bf6b..8cd1417 100644
--- a/src/Result.php
+++ b/src/Result.php
@@ -2,10 +2,6 @@
 
 namespace Cubicl\StructureCheck;
 
-/**
- * Class Result
- * @package Cubicl\StructureCheck
- */
 class Result implements ResultInterface
 {
 
@@ -15,7 +11,7 @@ class Result implements ResultInterface
     private $valid;
 
     /**
-     * @var array
+     * @var ErrorInterface[]
      */
     private $errors;
 
@@ -23,18 +19,33 @@ class Result implements ResultInterface
      * Result constructor.
      *
      * @param bool $valid
-     * @param array $errors
+     * @param ErrorInterface[] $errors
      */
-    public function __construct($valid, array $errors = [])
+    public function __construct($valid, array $errors)
     {
         $this->valid = $valid;
         $this->errors = $errors;
     }
 
+    public static function valid(): ResultInterface
+    {
+        return new self(true, []);
+    }
+
+    /**
+     * @param ErrorInterface[] $errors
+     *
+     * @return ResultInterface
+     */
+    public static function invalid(array $errors): ResultInterface
+    {
+        return new self(false, $errors);
+    }
+
     /**
      * @inheritdoc
      */
-    public function isValid()
+    public function isValid(): bool
     {
         return $this->valid;
     }
@@ -42,8 +53,8 @@ public function isValid()
     /**
      * @inheritdoc
      */
-    public function getErrors()
+    public function getErrors(): array
     {
         return $this->errors;
     }
-}
\ No newline at end of file
+}
diff --git a/src/ResultInterface.php b/src/ResultInterface.php
index dda5ac6..7bb0184 100644
--- a/src/ResultInterface.php
+++ b/src/ResultInterface.php
@@ -10,15 +10,13 @@ interface ResultInterface
 {
     /**
      * Returns TRUE if the check was successful.
-     *
-     * @return bool
      */
-    public function isValid();
+    public function isValid(): bool;
 
     /**
      * Returns a list of errors. If no error occurred, it will return an empty array.
      *
-     * @return array
+     * @return ErrorInterface[]
      */
-    public function getErrors();
-}
\ No newline at end of file
+    public function getErrors(): array;
+}
diff --git a/src/Type/AnyType.php b/src/Type/AnyType.php
index 11a441d..dc2b925 100644
--- a/src/Type/AnyType.php
+++ b/src/Type/AnyType.php
@@ -3,6 +3,7 @@
 namespace Cubicl\StructureCheck\Type;
 
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
 /**
  * Class AnyType
@@ -13,8 +14,8 @@ class AnyType implements TypeInterface
     /**
      * @inheritdoc
      */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        return new Result(true);
+        return Result::valid();
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/BoolType.php b/src/Type/BoolType.php
index 1cd5003..10bede9 100644
--- a/src/Type/BoolType.php
+++ b/src/Type/BoolType.php
@@ -2,29 +2,20 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class BoolType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class BoolType implements TypeInterface
 {
     private static $errorMessage = 'The value %s is not a boolean.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_bool($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/DatetimeType.php b/src/Type/DatetimeType.php
index 9e24770..f4e212b 100644
--- a/src/Type/DatetimeType.php
+++ b/src/Type/DatetimeType.php
@@ -2,15 +2,12 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use DateTime;
 use DateTimeZone;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class DatetimeType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class DatetimeType implements TypeInterface
 {
     /**
@@ -28,42 +25,26 @@ class DatetimeType implements TypeInterface
      */
     private $datetimeZone;
 
-    /**
-     * DatetimeType constructor.
-     *
-     * @param string $format
-     * @param string $datetimeZone
-     */
-    public function __construct($format, $datetimeZone)
+    public function __construct(string $format, string $datetimeZone)
     {
         $this->datetimeFormat = $format;
         $this->datetimeZone = $datetimeZone;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value) && $this->isValidDatetime($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
 
-    /**
-     * @param string $value
-     *
-     * @return bool
-     */
-    private function isValidDatetime($value) {
+    private function isValidDatetime(string $value): bool
+    {
         $date = DateTime::createFromFormat($this->datetimeFormat, $value, new DateTimeZone($this->datetimeZone));
-        $errors = DateTime::getLastErrors()["warning_count"];
+        $errors = DateTime::getLastErrors();
 
-        return $date && $errors["warning_count"] == 0 && $errors["error_count"] == 0;
+        return $date && $errors['warning_count'] === 0 && $errors['error_count'] === 0;
     }
 }
diff --git a/src/Type/EnumType.php b/src/Type/EnumType.php
index fa06419..f63f96d 100644
--- a/src/Type/EnumType.php
+++ b/src/Type/EnumType.php
@@ -2,20 +2,21 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
 class EnumType implements TypeInterface
 {
     /**
-     * @var array
+     * @var string
      */
-    private $values = [];
+    private static $errorMessage = 'The value %s is not in the allowed values (%s).';
 
     /**
-     * @var string
+     * @var array
      */
-    private static $errorMessage = 'The value %s is not in the allowed values (%s).';
+    private $values;
 
     /**
      * EnumType constructor.
@@ -27,18 +28,13 @@ public function __construct(array $values)
         $this->values = $values;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = in_array($value, $this->values, true);
-
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value), implode(',', $this->values))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), implode(',', $this->values)))
+            ]);
     }
 }
diff --git a/src/Type/ExactValueType.php b/src/Type/ExactValueType.php
index e1323c1..91c908d 100644
--- a/src/Type/ExactValueType.php
+++ b/src/Type/ExactValueType.php
@@ -2,12 +2,12 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
 class ExactValueType implements TypeInterface
 {
-
     /**
      * @var string
      */
@@ -26,18 +26,14 @@ public function __construct($value)
         $this->value = $value;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = $this->value === $value;
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value), $this->value)] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), json_encode($this->value)))
+            ]);
     }
 }
diff --git a/src/Type/FloatType.php b/src/Type/FloatType.php
index 49889fc..87c7eb0 100644
--- a/src/Type/FloatType.php
+++ b/src/Type/FloatType.php
@@ -2,22 +2,20 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
 class FloatType implements TypeInterface
 {
     private static $errorMessage = 'The value %s is not a float.';
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_float($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/IntType.php b/src/Type/IntType.php
index 2aaa8b4..7e4e036 100644
--- a/src/Type/IntType.php
+++ b/src/Type/IntType.php
@@ -2,29 +2,20 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class IntType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class IntType implements TypeInterface
 {
     private static $errorMessage = 'The value %s is not an integer.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_int($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/ListType.php b/src/Type/ListType.php
index 6d92ba7..0c5af64 100644
--- a/src/Type/ListType.php
+++ b/src/Type/ListType.php
@@ -2,12 +2,10 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class ListType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class ListType implements TypeInterface
 {
     private static $isNotAnArrayMessage = 'The given value %s is not an array.';
@@ -17,38 +15,32 @@ class ListType implements TypeInterface
      */
     private $child;
 
-    /**
-     * ListType constructor.
-     *
-     * @param TypeInterface $child
-     */
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         if (!is_array($value)) {
-            return new Result(
-                false,
-                [sprintf(self::$isNotAnArrayMessage, json_encode($value))]
+            return Result::invalid(
+                [new Error($key, sprintf(self::$isNotAnArrayMessage, json_encode($value)))]
             );
         }
 
         $errors = [];
         $valid = true;
 
-        foreach ($value as $item) {
-            $result = $this->child->check($item);
+        foreach ($value as $idx => $item) {
+            $result = $this->child->check(sprintf('%s.%d', $key, $idx), $item);
 
             $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }
 
-        return new Result($valid, $errors);
+        return $valid
+            ? Result::valid()
+            : Result::invalid($errors);
+
     }
 }
diff --git a/src/Type/NullableType.php b/src/Type/NullableType.php
index 6f4d06f..c66f5a4 100644
--- a/src/Type/NullableType.php
+++ b/src/Type/NullableType.php
@@ -3,38 +3,26 @@
 namespace Cubicl\StructureCheck\Type;
 
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class NullableType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class NullableType implements TypeInterface
 {
-
     /**
      * @var TypeInterface
      */
     private $child;
 
-    /**
-     * NullableType constructor.
-     *
-     * @param TypeInterface $child
-     */
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        if(is_null($value)) {
-            return new Result(true);
+        if($value === null) {
+            return Result::valid();
         }
 
-        return $this->child->check($value);
+        return $this->child->check($key, $value);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/NumericType.php b/src/Type/NumericType.php
index 68fa1c1..796f092 100644
--- a/src/Type/NumericType.php
+++ b/src/Type/NumericType.php
@@ -2,6 +2,7 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
@@ -9,18 +10,12 @@ class NumericType implements TypeInterface
 {
     private static $errorMessage = 'The value %s is not a numeric value.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_numeric($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
 }
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index da369b4..49a9fb6 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -2,7 +2,9 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
+use Cubicl\StructureCheck\ResultInterface;
 
 class ObjectType implements TypeInterface
 {
@@ -23,25 +25,23 @@ public function __construct(array $children)
         $this->children = $children;
     }
 
-    /**
-     * @inheritdoc
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $errors = [];
         $valid = true;
 
-        foreach ($this->children as $key => $child) {
-            if (!array_key_exists($key, $value)) {
+        foreach ($this->children as $objectProperty => $child) {
+            $fullKey = sprintf('%s.%s', $key, $objectProperty);
+            if (!array_key_exists($objectProperty, $value)) {
                 if (!$child instanceof OptionalType) {
                     $valid = false;
-                    $errors[] = sprintf(self::$missingKeyErrorMessage, $key);
+                    $errors[] = new Error($fullKey, sprintf(self::$missingKeyErrorMessage, $objectProperty));
                 }
 
                 continue;
             }
 
-            $result = $child->check($value[$key]);
+            $result = $child->check($fullKey, $value[$objectProperty]);
             $valid = $valid && $result->isValid();
             $errors += $result->getErrors();
         }
diff --git a/src/Type/OptionalType.php b/src/Type/OptionalType.php
index b300150..7b68ba4 100644
--- a/src/Type/OptionalType.php
+++ b/src/Type/OptionalType.php
@@ -4,34 +4,17 @@
 
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class OptionalType
- * @package Cubicl\Cubicl\StructureCheck\Type
- * @author Christian Blank <christian@cubicl.de>
- */
 class OptionalType implements TypeInterface
 {
-    /**
-     * @var TypeInterface
-     */
     private $child;
 
-    /**
-     * OptionalType constructor.
-     * @param TypeInterface $child
-     */
     public function __construct(TypeInterface $child)
     {
         $this->child = $child;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
-        return $this->child->check($value);
+        return $this->child->check($key, $value);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/RegexType.php b/src/Type/RegexType.php
index 6fb2888..84d5256 100644
--- a/src/Type/RegexType.php
+++ b/src/Type/RegexType.php
@@ -2,13 +2,10 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class RegexType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class RegexType implements TypeInterface
 {
     /**
@@ -21,28 +18,19 @@ class RegexType implements TypeInterface
      */
     private $regex;
 
-    /**
-     * RegexType constructor.
-     *
-     * @param string $regex
-     */
-    public function __construct($regex)
+    public function __construct(string $regex)
     {
         $this->regex = $regex;
     }
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value) && preg_match($this->regex, $value) === 1;
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value), $this->regex)] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([
+                new Error($key, sprintf(self::$errorMessage, json_encode($value), json_encode($this->regex)))
+            ]);
     }
 }
diff --git a/src/Type/StringType.php b/src/Type/StringType.php
index 9c69f2a..4e2441d 100644
--- a/src/Type/StringType.php
+++ b/src/Type/StringType.php
@@ -2,29 +2,20 @@
 
 namespace Cubicl\StructureCheck\Type;
 
+use Cubicl\StructureCheck\Error;
 use Cubicl\StructureCheck\Result;
 use Cubicl\StructureCheck\ResultInterface;
 
-/**
- * Class StringType
- * @package Cubicl\Cubicl\StructureCheck\Type
- */
 class StringType implements TypeInterface
 {
     private static $errorMessage = 'The value %s is not a string.';
 
-    /**
-     * @param mixed $value
-     *
-     * @return ResultInterface
-     */
-    public function check($value)
+    public function check(string $key, $value): ResultInterface
     {
         $checkResult = is_string($value);
 
-        return new Result(
-            $checkResult,
-            !$checkResult ? [sprintf(self::$errorMessage, json_encode($value))] : []
-        );
+        return $checkResult
+            ? Result::valid()
+            : Result::invalid([new Error($key, sprintf(self::$errorMessage, json_encode($value)))]);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Type/TypeInterface.php b/src/Type/TypeInterface.php
index 4ee25e5..450989c 100644
--- a/src/Type/TypeInterface.php
+++ b/src/Type/TypeInterface.php
@@ -11,9 +11,10 @@
 interface TypeInterface
 {
     /**
-     * @param mixed $value
+     * @param string $key
+     * @param mixed  $value
      *
      * @return ResultInterface
      */
-    public function check($value);
-}
\ No newline at end of file
+    public function check(string $key, $value): ResultInterface;
+}
diff --git a/tests/Integration/Type/ObjectTypeTest.php b/tests/Integration/Type/ObjectTypeTest.php
index 91a9592..0750194 100644
--- a/tests/Integration/Type/ObjectTypeTest.php
+++ b/tests/Integration/Type/ObjectTypeTest.php
@@ -24,7 +24,7 @@ class ObjectTypeTest extends TestCase
     /**
      *
      */
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
         $this->checker = new Checker();
@@ -33,14 +33,14 @@ protected function setUp()
     /**
      * @test
      */
-    public function itShouldHandleAbsenceOfOptionalDeclaredType()
+    public function itShouldHandleAbsenceOfOptionalDeclaredType(): void
     {
         $structure = new ObjectType([
             'opt' => new OptionalType(new AnyType())
         ]);
 
-        $actual = $structure->check([]);
+        $actual = $structure->check('', []);
 
         $this->assertSame(true, $actual->isValid());
     }
-}
\ No newline at end of file
+}