diff --git a/src/Date/DateInterval.php b/src/Date/DateInterval.php
index cdf4bbe..1eac6a2 100644
--- a/src/Date/DateInterval.php
+++ b/src/Date/DateInterval.php
@@ -159,7 +159,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(DateInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -183,7 +183,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(DateInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -195,7 +195,7 @@ public function intersects(DateInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(DateInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -207,7 +207,7 @@ public function intersection(DateInterval $interval)
      *
      * @return self
      */
-    public function cover(DateInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -219,7 +219,7 @@ public function cover(DateInterval $interval)
      *
      * @return self|null
      */
-    public function gap(DateInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -231,7 +231,7 @@ public function gap(DateInterval $interval)
      *
      * @return bool
      */
-    public function abuts(DateInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -243,7 +243,7 @@ public function abuts(DateInterval $interval)
      *
      * @return self|null
      */
-    public function join(DateInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -255,7 +255,7 @@ public function join(DateInterval $interval)
      *
      * @return self|null
      */
-    public function union(DateInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/DateTime/DateTimeInterval.php b/src/DateTime/DateTimeInterval.php
index 835b039..d1e6b0a 100644
--- a/src/DateTime/DateTimeInterval.php
+++ b/src/DateTime/DateTimeInterval.php
@@ -159,7 +159,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(DateTimeInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -183,7 +183,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(DateTimeInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -195,7 +195,7 @@ public function intersects(DateTimeInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(DateTimeInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -207,7 +207,7 @@ public function intersection(DateTimeInterval $interval)
      *
      * @return self
      */
-    public function cover(DateTimeInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -219,7 +219,7 @@ public function cover(DateTimeInterval $interval)
      *
      * @return self|null
      */
-    public function gap(DateTimeInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -231,7 +231,7 @@ public function gap(DateTimeInterval $interval)
      *
      * @return bool
      */
-    public function abuts(DateTimeInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -243,7 +243,7 @@ public function abuts(DateTimeInterval $interval)
      *
      * @return self|null
      */
-    public function join(DateTimeInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -255,7 +255,7 @@ public function join(DateTimeInterval $interval)
      *
      * @return self|null
      */
-    public function union(DateTimeInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/IPv4/IPv4Interval.php b/src/IPv4/IPv4Interval.php
index f8fb5df..17ccf3b 100644
--- a/src/IPv4/IPv4Interval.php
+++ b/src/IPv4/IPv4Interval.php
@@ -156,7 +156,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(IPv4Interval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -180,7 +180,7 @@ public function contains($point)
      *
      * @return bool
      */
-    public function intersects(IPv4Interval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -192,7 +192,7 @@ public function intersects(IPv4Interval $interval)
      *
      * @return self|null
      */
-    public function intersection(IPv4Interval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -204,7 +204,7 @@ public function intersection(IPv4Interval $interval)
      *
      * @return self
      */
-    public function cover(IPv4Interval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -216,7 +216,7 @@ public function cover(IPv4Interval $interval)
      *
      * @return self|null
      */
-    public function gap(IPv4Interval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -228,7 +228,7 @@ public function gap(IPv4Interval $interval)
      *
      * @return bool
      */
-    public function abuts(IPv4Interval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -240,7 +240,7 @@ public function abuts(IPv4Interval $interval)
      *
      * @return self|null
      */
-    public function join(IPv4Interval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -252,7 +252,7 @@ public function join(IPv4Interval $interval)
      *
      * @return self|null
      */
-    public function union(IPv4Interval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/IPv4Network/IPv4Network.php b/src/IPv4Network/IPv4Network.php
index d2ccaf4..a1833bc 100644
--- a/src/IPv4Network/IPv4Network.php
+++ b/src/IPv4Network/IPv4Network.php
@@ -120,7 +120,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(IPv4Network $network)
+    public function equal(self $network)
     {
         return $this->comparator->equal($network);
     }
@@ -144,7 +144,7 @@ public function contains($point)
      *
      * @return bool
      */
-    public function intersects(IPv4Network $network)
+    public function intersects(self $network)
     {
         return $this->comparator->intersects($network);
     }
@@ -156,7 +156,7 @@ public function intersects(IPv4Network $network)
      *
      * @return bool
      */
-    public function abuts(IPv4Network $network)
+    public function abuts(self $network)
     {
         return $this->comparator->abuts($network);
     }
diff --git a/src/IPv4Network/IPv4NetworkMask.php b/src/IPv4Network/IPv4NetworkMask.php
index 3323e53..084ceb5 100644
--- a/src/IPv4Network/IPv4NetworkMask.php
+++ b/src/IPv4Network/IPv4NetworkMask.php
@@ -108,7 +108,7 @@ public function cidr()
      *
      * @return bool
      */
-    public function equal(IPv4NetworkMask $mask)
+    public function equal(self $mask)
     {
         return $this->long == $mask->ip();
     }
diff --git a/src/IPv6/IPv6Interval.php b/src/IPv6/IPv6Interval.php
index 8a587bb..133f0fb 100644
--- a/src/IPv6/IPv6Interval.php
+++ b/src/IPv6/IPv6Interval.php
@@ -144,6 +144,7 @@ public static function fromString($string)
     {
         if (!preg_match(self::REGEXP, $string, $match)) {
             $ipv6 = implode(':', array_fill(0, 8, 'ffff'));
+
             throw InvalidIntervalFormatException::create(sprintf('[%s, %s]', $ipv6, $ipv6), $string);
         }
 
@@ -157,7 +158,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(IPv6Interval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -181,7 +182,7 @@ public function contains($point)
      *
      * @return bool
      */
-    public function intersects(IPv6Interval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -193,7 +194,7 @@ public function intersects(IPv6Interval $interval)
      *
      * @return self|null
      */
-    public function intersection(IPv6Interval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -205,7 +206,7 @@ public function intersection(IPv6Interval $interval)
      *
      * @return self
      */
-    public function cover(IPv6Interval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -217,7 +218,7 @@ public function cover(IPv6Interval $interval)
      *
      * @return self|null
      */
-    public function gap(IPv6Interval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -229,7 +230,7 @@ public function gap(IPv6Interval $interval)
      *
      * @return bool
      */
-    public function abuts(IPv6Interval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -241,7 +242,7 @@ public function abuts(IPv6Interval $interval)
      *
      * @return self|null
      */
-    public function join(IPv6Interval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -253,7 +254,7 @@ public function join(IPv6Interval $interval)
      *
      * @return self|null
      */
-    public function union(IPv6Interval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/IPv6Network/IPv6Network.php b/src/IPv6Network/IPv6Network.php
index c75c3a9..dbf5600 100644
--- a/src/IPv6Network/IPv6Network.php
+++ b/src/IPv6Network/IPv6Network.php
@@ -117,6 +117,7 @@ public static function fromString($string)
     {
         if (!preg_match(self::REGEXP, $string, $match)) {
             $ipv6 = implode(':', array_fill(0, 8, 'ffff'));
+
             throw InvalidIntervalFormatException::create($ipv6.'/128', $string);
         }
 
@@ -130,7 +131,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(IPv6Network $network)
+    public function equal(self $network)
     {
         return $this->comparator->equal($network);
     }
@@ -154,7 +155,7 @@ public function contains($point)
      *
      * @return bool
      */
-    public function intersects(IPv6Network $network)
+    public function intersects(self $network)
     {
         return $this->comparator->intersects($network);
     }
@@ -166,7 +167,7 @@ public function intersects(IPv6Network $network)
      *
      * @return bool
      */
-    public function abuts(IPv6Network $network)
+    public function abuts(self $network)
     {
         return $this->comparator->abuts($network);
     }
diff --git a/src/IntervalPointInterface.php b/src/IntervalPointInterface.php
index f1e8c17..416eb1b 100644
--- a/src/IntervalPointInterface.php
+++ b/src/IntervalPointInterface.php
@@ -22,42 +22,42 @@ public function value();
      *
      * @return bool
      */
-    public function eq(IntervalPointInterface $point);
+    public function eq(self $point);
 
     /**
      * @param IntervalPointInterface $point
      *
      * @return bool
      */
-    public function neq(IntervalPointInterface $point);
+    public function neq(self $point);
 
     /**
      * @param IntervalPointInterface $point
      *
      * @return bool
      */
-    public function lt(IntervalPointInterface $point);
+    public function lt(self $point);
 
     /**
      * @param IntervalPointInterface $point
      *
      * @return bool
      */
-    public function lte(IntervalPointInterface $point);
+    public function lte(self $point);
 
     /**
      * @param IntervalPointInterface $point
      *
      * @return bool
      */
-    public function gt(IntervalPointInterface $point);
+    public function gt(self $point);
 
     /**
      * @param IntervalPointInterface $point
      *
      * @return bool
      */
-    public function gte(IntervalPointInterface $point);
+    public function gte(self $point);
 
     /**
      * @return string
diff --git a/src/IntervalType.php b/src/IntervalType.php
index 9a051f8..f8203f4 100644
--- a/src/IntervalType.php
+++ b/src/IntervalType.php
@@ -228,7 +228,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(IntervalType $type)
+    public function equal(self $type)
     {
         return $this->type() == $type->type();
     }
diff --git a/src/Month/MonthInterval.php b/src/Month/MonthInterval.php
index 8ab29f9..fa7bb2e 100644
--- a/src/Month/MonthInterval.php
+++ b/src/Month/MonthInterval.php
@@ -160,7 +160,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(MonthInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -184,7 +184,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(MonthInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -196,7 +196,7 @@ public function intersects(MonthInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(MonthInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -208,7 +208,7 @@ public function intersection(MonthInterval $interval)
      *
      * @return self
      */
-    public function cover(MonthInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -220,7 +220,7 @@ public function cover(MonthInterval $interval)
      *
      * @return self|null
      */
-    public function gap(MonthInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -232,7 +232,7 @@ public function gap(MonthInterval $interval)
      *
      * @return bool
      */
-    public function abuts(MonthInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -244,7 +244,7 @@ public function abuts(MonthInterval $interval)
      *
      * @return self|null
      */
-    public function join(MonthInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -256,7 +256,7 @@ public function join(MonthInterval $interval)
      *
      * @return self|null
      */
-    public function union(MonthInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/Number/NumberInterval.php b/src/Number/NumberInterval.php
index b1a546f..ef0a3f4 100644
--- a/src/Number/NumberInterval.php
+++ b/src/Number/NumberInterval.php
@@ -156,7 +156,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(NumberInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -180,7 +180,7 @@ public function contains($point)
      *
      * @return bool
      */
-    public function intersects(NumberInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -192,7 +192,7 @@ public function intersects(NumberInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(NumberInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -204,7 +204,7 @@ public function intersection(NumberInterval $interval)
      *
      * @return self
      */
-    public function cover(NumberInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -216,7 +216,7 @@ public function cover(NumberInterval $interval)
      *
      * @return self|null
      */
-    public function gap(NumberInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -228,7 +228,7 @@ public function gap(NumberInterval $interval)
      *
      * @return bool
      */
-    public function abuts(NumberInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -240,7 +240,7 @@ public function abuts(NumberInterval $interval)
      *
      * @return self|null
      */
-    public function join(NumberInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -252,7 +252,7 @@ public function join(NumberInterval $interval)
      *
      * @return self|null
      */
-    public function union(NumberInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/Time/TimeInterval.php b/src/Time/TimeInterval.php
index 6942639..e948211 100644
--- a/src/Time/TimeInterval.php
+++ b/src/Time/TimeInterval.php
@@ -160,7 +160,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(TimeInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -184,7 +184,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(TimeInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -196,7 +196,7 @@ public function intersects(TimeInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(TimeInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -208,7 +208,7 @@ public function intersection(TimeInterval $interval)
      *
      * @return self
      */
-    public function cover(TimeInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -220,7 +220,7 @@ public function cover(TimeInterval $interval)
      *
      * @return self|null
      */
-    public function gap(TimeInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -232,7 +232,7 @@ public function gap(TimeInterval $interval)
      *
      * @return bool
      */
-    public function abuts(TimeInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -244,7 +244,7 @@ public function abuts(TimeInterval $interval)
      *
      * @return self|null
      */
-    public function join(TimeInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -256,7 +256,7 @@ public function join(TimeInterval $interval)
      *
      * @return self|null
      */
-    public function union(TimeInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/Week/WeekInterval.php b/src/Week/WeekInterval.php
index e45d6aa..85acda2 100644
--- a/src/Week/WeekInterval.php
+++ b/src/Week/WeekInterval.php
@@ -160,7 +160,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(WeekInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -184,7 +184,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(WeekInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -196,7 +196,7 @@ public function intersects(WeekInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(WeekInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -208,7 +208,7 @@ public function intersection(WeekInterval $interval)
      *
      * @return self
      */
-    public function cover(WeekInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -220,7 +220,7 @@ public function cover(WeekInterval $interval)
      *
      * @return self|null
      */
-    public function gap(WeekInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -232,7 +232,7 @@ public function gap(WeekInterval $interval)
      *
      * @return bool
      */
-    public function abuts(WeekInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -244,7 +244,7 @@ public function abuts(WeekInterval $interval)
      *
      * @return self|null
      */
-    public function join(WeekInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -256,7 +256,7 @@ public function join(WeekInterval $interval)
      *
      * @return self|null
      */
-    public function union(WeekInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/src/Year/YearInterval.php b/src/Year/YearInterval.php
index 47fb3b5..f06cdfd 100644
--- a/src/Year/YearInterval.php
+++ b/src/Year/YearInterval.php
@@ -160,7 +160,7 @@ public static function fromString($string)
      *
      * @return bool
      */
-    public function equal(YearInterval $interval)
+    public function equal(self $interval)
     {
         return $this->comparator->equal($interval);
     }
@@ -184,7 +184,7 @@ public function contains(\DateTime $point)
      *
      * @return bool
      */
-    public function intersects(YearInterval $interval)
+    public function intersects(self $interval)
     {
         return $this->comparator->intersects($interval);
     }
@@ -196,7 +196,7 @@ public function intersects(YearInterval $interval)
      *
      * @return self|null
      */
-    public function intersection(YearInterval $interval)
+    public function intersection(self $interval)
     {
         return $this->comparator->intersection($interval);
     }
@@ -208,7 +208,7 @@ public function intersection(YearInterval $interval)
      *
      * @return self
      */
-    public function cover(YearInterval $interval)
+    public function cover(self $interval)
     {
         return $this->comparator->cover($interval);
     }
@@ -220,7 +220,7 @@ public function cover(YearInterval $interval)
      *
      * @return self|null
      */
-    public function gap(YearInterval $interval)
+    public function gap(self $interval)
     {
         return $this->comparator->gap($interval);
     }
@@ -232,7 +232,7 @@ public function gap(YearInterval $interval)
      *
      * @return bool
      */
-    public function abuts(YearInterval $interval)
+    public function abuts(self $interval)
     {
         return $this->comparator->abuts($interval);
     }
@@ -244,7 +244,7 @@ public function abuts(YearInterval $interval)
      *
      * @return self|null
      */
-    public function join(YearInterval $interval)
+    public function join(self $interval)
     {
         return $this->comparator->join($interval);
     }
@@ -256,7 +256,7 @@ public function join(YearInterval $interval)
      *
      * @return self|null
      */
-    public function union(YearInterval $interval)
+    public function union(self $interval)
     {
         return $this->comparator->union($interval);
     }
diff --git a/tests/IPv6/IPv6IntervalTest.php b/tests/IPv6/IPv6IntervalTest.php
index 3880b8a..25b3269 100644
--- a/tests/IPv6/IPv6IntervalTest.php
+++ b/tests/IPv6/IPv6IntervalTest.php
@@ -66,15 +66,19 @@ public function testFromString($start, $end, $type)
         switch ($type) {
             case IntervalType::TYPE_CLOSED:
                 $interval3 = IPv6Interval::closed($start, $end);
+
                 break;
             case IntervalType::TYPE_OPEN:
                 $interval3 = IPv6Interval::open($start, $end);
+
                 break;
             case IntervalType::TYPE_HALF_CLOSED:
                 $interval3 = IPv6Interval::halfClosed($start, $end);
+
                 break;
             case IntervalType::TYPE_HALF_OPEN:
                 $interval3 = IPv6Interval::halfOpen($start, $end);
+
                 break;
             default: // bad interval type
                 $interval3 = null;