diff --git a/DataStorage/Database/Query/Builder.php b/DataStorage/Database/Query/Builder.php
index 9257606a6..3da86dab5 100644
--- a/DataStorage/Database/Query/Builder.php
+++ b/DataStorage/Database/Query/Builder.php
@@ -263,7 +263,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function select(...$columns) : Builder
+    public function select(...$columns) : self
     {
         $this->type = QueryType::SELECT;
 
@@ -289,7 +289,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function random(...$columns) : Builder
+    public function random(...$columns) : self
     {
         $this->select(...$columns);
 
@@ -307,7 +307,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function bind($binds) : Builder
+    public function bind($binds) : self
     {
         if (\is_array($binds)) {
             $this->binds += $binds;
@@ -327,7 +327,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function newQuery() : Builder
+    public function newQuery() : self
     {
         return new static($this->connection, $this->isReadOnly);
     }
@@ -355,7 +355,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function raw(string $raw) : Builder
+    public function raw(string $raw) : self
     {
         if (!$this->isValidReadOnly($raw)) {
             throw new \Exception();
@@ -405,7 +405,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function selectRaw($expression) : Builder
+    public function selectRaw($expression) : self
     {
         $this->selects[null][] = $expression;
 
@@ -419,7 +419,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function distinct() : Builder
+    public function distinct() : self
     {
         $this->distinct = true;
 
@@ -435,7 +435,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function from(...$tables) : Builder
+    public function from(...$tables) : self
     {
         foreach ($tables as $key => $table) {
             if (\is_string($table) || $table instanceof \Closure) {
@@ -457,7 +457,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function fromRaw($expression) : Builder
+    public function fromRaw($expression) : self
     {
         $this->from[null][] = $expression;
 
@@ -478,7 +478,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function where($columns, $operator = null, $values = null, $boolean = 'and') : Builder
+    public function where($columns, $operator = null, $values = null, $boolean = 'and') : self
     {
         if (!\is_array($columns)) {
             $columns  = [$columns];
@@ -534,7 +534,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function andWhere($where, $operator = null, $values = null) : Builder
+    public function andWhere($where, $operator = null, $values = null) : self
     {
         return $this->where($where, $operator, $values, 'and');
     }
@@ -550,7 +550,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function orWhere($where, $operator = null, $values = null) : Builder
+    public function orWhere($where, $operator = null, $values = null) : self
     {
         return $this->where($where, $operator, $values, 'or');
     }
@@ -566,7 +566,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function whereIn($column, $values = null, string $boolean = 'and') : Builder
+    public function whereIn($column, $values = null, string $boolean = 'and') : self
     {
         $this->where($column, 'in', $values, $boolean);
 
@@ -583,7 +583,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function whereNull($column, string $boolean = 'and') : Builder
+    public function whereNull($column, string $boolean = 'and') : self
     {
         $this->where($column, '=', null, $boolean);
 
@@ -600,7 +600,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function whereNotNull($column, string $boolean = 'and') : Builder
+    public function whereNotNull($column, string $boolean = 'and') : self
     {
         $this->where($column, '!=', null, $boolean);
 
@@ -616,7 +616,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function groupBy(...$columns) : Builder
+    public function groupBy(...$columns) : self
     {
         foreach ($columns as $key => $column) {
             if (\is_string($column) || $column instanceof \Closure) {
@@ -638,7 +638,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function newest($column) : Builder
+    public function newest($column) : self
     {
         $this->orderBy($column, 'DESC');
 
@@ -654,7 +654,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function oldest($column) : Builder
+    public function oldest($column) : self
     {
         $this->orderBy($column, 'ASC');
 
@@ -671,7 +671,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function orderBy($columns, $order = 'DESC') : Builder
+    public function orderBy($columns, $order = 'DESC') : self
     {
         if (\is_string($columns) || $columns instanceof \Closure) {
             if (!\is_string($order)) {
@@ -703,7 +703,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function offset(int $offset) : Builder
+    public function offset(int $offset) : self
     {
         $this->offset = $offset;
 
@@ -719,7 +719,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function limit(int $limit) : Builder
+    public function limit(int $limit) : self
     {
         $this->limit = $limit;
 
@@ -735,7 +735,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function union($query) : Builder
+    public function union($query) : self
     {
         if (!\is_array($query)) {
             $this->unions[] = $query;
@@ -800,7 +800,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function count(string $table = '*') : Builder
+    public function count(string $table = '*') : self
     {
         // todo: don't do this as string, create new object new \count(); this can get handled by the grammar parser WAY better
         return $this->select('COUNT(' . $table . ')');
@@ -861,7 +861,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function insert(...$columns) : Builder
+    public function insert(...$columns) : self
     {
         if ($this->isReadOnly) {
             throw new \Exception();
@@ -885,7 +885,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function into($table) : Builder
+    public function into($table) : self
     {
         $this->into = $table;
 
@@ -901,7 +901,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function values(...$values) : Builder
+    public function values(...$values) : self
     {
         $this->values[] = $values;
 
@@ -929,7 +929,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function value($value) : Builder
+    public function value($value) : self
     {
         \end($this->values);
         $key = \key($this->values);
@@ -954,7 +954,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function sets(...$sets) : Builder
+    public function sets(...$sets) : self
     {
         $this->sets[$sets[0]] = $sets[1] ?? null;
 
@@ -970,7 +970,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function set($set) : Builder
+    public function set($set) : self
     {
         $this->sets[\key($set)] = \current($set);
 
@@ -988,7 +988,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function update(...$tables) : Builder
+    public function update(...$tables) : self
     {
         if ($this->isReadOnly) {
             throw new \Exception();
@@ -1014,7 +1014,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function delete() : Builder
+    public function delete() : self
     {
         if ($this->isReadOnly) {
             throw new \Exception();
@@ -1054,7 +1054,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function join($table, string $type = JoinType::JOIN) : Builder
+    public function join($table, string $type = JoinType::JOIN) : self
     {
         if (\is_string($table) || $table instanceof \Closure) {
             $this->joins[] = ['type' => $type, 'table' => $table];
@@ -1072,7 +1072,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function leftJoin($column) : Builder
+    public function leftJoin($column) : self
     {
         return $this->join($column, JoinType::LEFT_JOIN);
     }
@@ -1084,7 +1084,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function leftOuterJoin($column) : Builder
+    public function leftOuterJoin($column) : self
     {
         return $this->join($column, JoinType::LEFT_OUTER_JOIN);
     }
@@ -1096,7 +1096,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function leftInnerJoin($column) : Builder
+    public function leftInnerJoin($column) : self
     {
         return $this->join($column, JoinType::LEFT_INNER_JOIN);
     }
@@ -1108,7 +1108,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function rightJoin($column) : Builder
+    public function rightJoin($column) : self
     {
         return $this->join($column, JoinType::RIGHT_JOIN);
     }
@@ -1120,7 +1120,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function rightOuterJoin($column) : Builder
+    public function rightOuterJoin($column) : self
     {
         return $this->join($column, JoinType::RIGHT_OUTER_JOIN);
     }
@@ -1132,7 +1132,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function rightInnerJoin($column) : Builder
+    public function rightInnerJoin($column) : self
     {
         return $this->join($column, JoinType::RIGHT_INNER_JOIN);
     }
@@ -1144,7 +1144,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function outerJoin($column) : Builder
+    public function outerJoin($column) : self
     {
         return $this->join($column, JoinType::OUTER_JOIN);
     }
@@ -1156,7 +1156,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function innerJoin($column) : Builder
+    public function innerJoin($column) : self
     {
         return $this->join($column, JoinType::INNER_JOIN);
     }
@@ -1168,7 +1168,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function crossJoin($column) : Builder
+    public function crossJoin($column) : self
     {
         return $this->join($column, JoinType::CROSS_JOIN);
     }
@@ -1180,7 +1180,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function fullJoin($column) : Builder
+    public function fullJoin($column) : self
     {
         return $this->join($column, JoinType::FULL_JOIN);
     }
@@ -1192,7 +1192,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function fullOuterJoin($column) : Builder
+    public function fullOuterJoin($column) : self
     {
         return $this->join($column, JoinType::FULL_OUTER_JOIN);
     }
@@ -1204,7 +1204,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function rollback() : Builder
+    public function rollback() : self
     {
         return $this;
     }
@@ -1216,7 +1216,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function on($columns, $operator = null, $values = null, $boolean = 'and') : Builder
+    public function on($columns, $operator = null, $values = null, $boolean = 'and') : self
     {
         if ($operator !== null && !\is_array($operator) && !\in_array(\strtolower($operator), self::OPERATORS)) {
             throw new \InvalidArgumentException('Unknown operator.');
@@ -1257,7 +1257,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function orOn($columns, $operator = null, $values = null) : Builder
+    public function orOn($columns, $operator = null, $values = null) : self
     {
         return $this->on($columns, $operator, $values, 'or');
     }
@@ -1269,7 +1269,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function andOn($columns, $operator = null, $values = null) : Builder
+    public function andOn($columns, $operator = null, $values = null) : self
     {
         return $this->on($columns, $operator, $values, 'and');
     }
@@ -1285,7 +1285,7 @@ class Builder extends BuilderAbstract
      *
      * @since  1.0.0
      */
-    public function merge(Builder $query) : Builder
+    public function merge(self $query) : self
     {
         return clone($this);
     }
diff --git a/DataStorage/Database/Schema/Builder.php b/DataStorage/Database/Schema/Builder.php
index 6595ee5da..40b24532f 100644
--- a/DataStorage/Database/Schema/Builder.php
+++ b/DataStorage/Database/Schema/Builder.php
@@ -46,7 +46,7 @@ class Builder extends QueryBuilder
         $this->grammar    = $connection->getSchemaGrammar();
     }
 
-    public function drop(...$table) : Builder
+    public function drop(...$table) : self
     {
         $this->type  = QueryType::DROP;
         $this->drop += $table;
@@ -55,14 +55,14 @@ class Builder extends QueryBuilder
         return $this;
     }
 
-    public function selectTables() : Builder
+    public function selectTables() : self
     {
         $this->type = QueryType::TABLES;
 
         return $this;
     }
 
-    public function selectFields(string $table) : Builder
+    public function selectFields(string $table) : self
     {
         $this->type = QueryType::FIELDS;
 
diff --git a/Localization/Money.php b/Localization/Money.php
index d911c3e6a..899f5f4ad 100644
--- a/Localization/Money.php
+++ b/Localization/Money.php
@@ -140,7 +140,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function setLocalization(string $thousands = ',', string $decimal = '.', string $symbol = '', int $position = 0) : Money
+    public function setLocalization(string $thousands = ',', string $decimal = '.', string $symbol = '', int $position = 0) : self
     {
         $this->thousands = $thousands;
         $this->decimal   = $decimal;
@@ -159,7 +159,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function setString(string $value) : Money
+    public function setString(string $value) : self
     {
         $this->value = self::toInt($value, $this->thousands, $this->decimal);
 
@@ -211,13 +211,13 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function add($value) : Money
+    public function add($value) : self
     {
         if (\is_string($value) || is_float($value)) {
             $this->value += self::toInt((string) $value, $this->thousands, $this->decimal);
         } elseif (\is_int($value)) {
             $this->value += $value;
-        } elseif ($value instanceof Money) {
+        } elseif ($value instanceof self) {
             $this->value += $value->getInt();
         }
 
@@ -245,13 +245,13 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function sub($value) : Money
+    public function sub($value) : self
     {
         if (\is_string($value) || is_float($value)) {
             $this->value -= self::toInt((string) $value, $this->thousands, $this->decimal);
         } elseif (\is_int($value)) {
             $this->value -= $value;
-        } elseif ($value instanceof Money) {
+        } elseif ($value instanceof self) {
             $this->value -= $value->getInt();
         }
 
@@ -267,7 +267,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function mult($value) : Money
+    public function mult($value) : self
     {
         if (\is_float($value) || is_int($value)) {
             $this->value = (int) ($this->value * $value);
@@ -285,7 +285,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function div($value) : Money
+    public function div($value) : self
     {
         if (\is_float($value) || is_int($value)) {
             $this->value = (int) ($this->value / $value);
@@ -301,7 +301,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function abs() : Money
+    public function abs() : self
     {
         $this->value = \abs($this->value);
 
@@ -317,7 +317,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function pow($value) : Money
+    public function pow($value) : self
     {
         if (\is_float($value) || is_int($value)) {
             $this->value = (int) ($this->value ** $value);
@@ -361,7 +361,7 @@ final class Money implements \Serializable
      *
      * @since  1.0.0
      */
-    public function setInt(int $value) : Money
+    public function setInt(int $value) : self
     {
         $this->value = $value;
 
diff --git a/Log/FileLogger.php b/Log/FileLogger.php
index 2187c7490..24a3505d5 100644
--- a/Log/FileLogger.php
+++ b/Log/FileLogger.php
@@ -135,7 +135,7 @@ final class FileLogger implements LoggerInterface
      *
      * @since  1.0.0
      */
-    public static function getInstance(string $path = '', bool $verbose = false) : FileLogger
+    public static function getInstance(string $path = '', bool $verbose = false) : self
     {
         if (self::$instance === null) {
             self::$instance = new self($path, $verbose);
diff --git a/Math/Geometry/Shape/D3/Sphere.php b/Math/Geometry/Shape/D3/Sphere.php
index a4dd6da3a..42f87e796 100644
--- a/Math/Geometry/Shape/D3/Sphere.php
+++ b/Math/Geometry/Shape/D3/Sphere.php
@@ -86,7 +86,7 @@ final class Sphere implements D3ShapeInterface
      *
      * @since  1.0.0
      */
-    public static function byRadius(float $r) : Sphere
+    public static function byRadius(float $r) : self
     {
         return new self($r);
     }
@@ -100,7 +100,7 @@ final class Sphere implements D3ShapeInterface
      *
      * @since  1.0.0
      */
-    public static function byVolume(float $v) : Sphere
+    public static function byVolume(float $v) : self
     {
         return new self(self::getRadiusByVolume($v));
     }
@@ -128,7 +128,7 @@ final class Sphere implements D3ShapeInterface
      *
      * @since  1.0.0
      */
-    public static function bySurface(float $s) : Sphere
+    public static function bySurface(float $s) : self
     {
         return new self(self::getRadiusBySurface($s));
     }
diff --git a/Math/Matrix/Matrix.php b/Math/Matrix/Matrix.php
index 4ab836880..dc5110ca3 100644
--- a/Math/Matrix/Matrix.php
+++ b/Math/Matrix/Matrix.php
@@ -126,9 +126,9 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function transpose() : Matrix
+    public function transpose() : self
     {
-        $matrix = new Matrix($this->n, $this->m);
+        $matrix = new self($this->n, $this->m);
         $matrix->setMatrix(\array_map(null, ...$this->matrix));
 
         return $matrix;
@@ -158,7 +158,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function getSubMatrix(int $iRow, int $lRow, int $iCol, int $lCol) : Matrix
+    public function getSubMatrix(int $iRow, int $lRow, int $iCol, int $lCol) : self
     {
         $X = [[]];
         for ($i = $iRow; $i <= $lRow; ++$i) {
@@ -183,7 +183,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function getSubMatrixByColumnsRows(array $rows, array $cols) : Matrix
+    public function getSubMatrixByColumnsRows(array $rows, array $cols) : self
     {
         $X       = [[]];
         $rlength = \count($rows);
@@ -212,7 +212,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function getSubMatrixByColumns(int $iRow, int $lRow, array $cols) : Matrix
+    public function getSubMatrixByColumns(int $iRow, int $lRow, array $cols) : self
     {
         $X      = [[]];
         $length = \count($cols);
@@ -240,7 +240,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function getSubMatrixByRows(array $rows, int $iCol, int $lCol) : Matrix
+    public function getSubMatrixByRows(array $rows, int $iCol, int $lCol) : self
     {
         $X      = [[]];
         $length = \count($rows);
@@ -378,7 +378,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function setMatrix(array $matrix) : Matrix
+    public function setMatrix(array $matrix) : self
     {
         $this->m      = \count($matrix);
         $this->n      = !\is_array($matrix[0] ?? 1) ? 1 : \count($matrix[0]);
@@ -398,9 +398,9 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function sub($value) : Matrix
+    public function sub($value) : self
     {
-        if ($value instanceof Matrix) {
+        if ($value instanceof self) {
             return $this->add($value->mult(-1));
         } elseif (!is_string($value) && is_numeric($value)) {
             return $this->add(-$value);
@@ -420,9 +420,9 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function add($value) : Matrix
+    public function add($value) : self
     {
-        if ($value instanceof Matrix) {
+        if ($value instanceof self) {
             return $this->addMatrix($value);
         } elseif (!is_string($value) && is_numeric($value)) {
             return $this->addScalar($value);
@@ -442,7 +442,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    private function addMatrix(Matrix $matrix) : Matrix
+    private function addMatrix(self $matrix) : self
     {
         if ($this->m !== $matrix->getM() || $this->n !== $matrix->getN()) {
             throw new InvalidDimensionException($matrix->getM() . 'x' . $matrix->getN());
@@ -457,7 +457,7 @@ class Matrix implements \ArrayAccess, \Iterator
             }
         }
 
-        $newMatrix = new Matrix($this->m, $this->n);
+        $newMatrix = new self($this->m, $this->n);
         $newMatrix->setMatrix($newMatrixArr);
 
         return $newMatrix;
@@ -498,7 +498,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    private function addScalar($scalar) : Matrix
+    private function addScalar($scalar) : self
     {
         $newMatrixArr = $this->matrix;
 
@@ -508,7 +508,7 @@ class Matrix implements \ArrayAccess, \Iterator
             }
         }
 
-        $newMatrix = new Matrix($this->m, $this->n);
+        $newMatrix = new self($this->m, $this->n);
         $newMatrix->setMatrix($newMatrixArr);
 
         return $newMatrix;
@@ -525,9 +525,9 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function mult($value) : Matrix
+    public function mult($value) : self
     {
-        if ($value instanceof Matrix) {
+        if ($value instanceof self) {
             return $this->multMatrix($value);
         } elseif (!is_string($value) && is_numeric($value)) {
             return $this->multScalar($value);
@@ -547,13 +547,13 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    private function multMatrix(Matrix $matrix) : Matrix
+    private function multMatrix(self $matrix) : self
     {
         $nDim = $matrix->getN();
         $mDim = $matrix->getM();
 
         $matrixArr    = $matrix->getMatrix();
-        $newMatrix    = new Matrix($this->m, $nDim);
+        $newMatrix    = new self($this->m, $nDim);
         $newMatrixArr = $newMatrix->getMatrix();
 
         for ($i = 0; $i < $this->m; ++$i) { // Row of $this
@@ -584,7 +584,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    private function multScalar($scalar) : Matrix
+    private function multScalar($scalar) : self
     {
         $newMatrixArr = $this->matrix;
 
@@ -594,7 +594,7 @@ class Matrix implements \ArrayAccess, \Iterator
             }
         }
 
-        $newMatrix = new Matrix($this->m, $this->n);
+        $newMatrix = new self($this->m, $this->n);
         $newMatrix->setMatrix($newMatrixArr);
 
         return $newMatrix;
@@ -607,9 +607,9 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function upperTriangular() : Matrix
+    public function upperTriangular() : self
     {
-        $matrix = new Matrix($this->n, $this->n);
+        $matrix = new self($this->n, $this->n);
 
         $matrixArr = $this->matrix;
         $this->upperTrianglize($matrixArr);
@@ -677,7 +677,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function inverse() : Matrix
+    public function inverse() : self
     {
         return $this->solve(new IdentityMatrix($this->m));
     }
@@ -691,7 +691,7 @@ class Matrix implements \ArrayAccess, \Iterator
      *
      * @since  1.0.0
      */
-    public function solve(Matrix $B) : Matrix
+    public function solve(self $B) : self
     {
         $M = $this->m === $this->n ? new LUDecomposition($this) : new QRDecomposition($this);
 
diff --git a/Math/Number/Complex.php b/Math/Number/Complex.php
index 585bddded..d519a25d8 100644
--- a/Math/Number/Complex.php
+++ b/Math/Number/Complex.php
@@ -87,7 +87,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function conjugate() : Complex
+    public function conjugate() : self
     {
         return new self($this->re, -$this->im);
     }
@@ -99,7 +99,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function reciprocal() : Complex
+    public function reciprocal() : self
     {
         return new self(
             $this->re / ($this->re ** 2 + $this->im ** 2),
@@ -114,7 +114,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function sqrt() : Complex
+    public function sqrt() : self
     {
         return new self(
             \sqrt(($this->re + \sqrt($this->re ** 2 + $this->im ** 2)) / 2),
@@ -141,25 +141,25 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function square() : Complex
+    public function square() : self
     {
         return $this->multComplex($this);
     }
 
-    public function pow($value) : Complex
+    public function pow($value) : self
     {
         if (\is_int($value)) {
             return $this->powInteger($value);
         } elseif (\is_numeric($value)) {
             return $this->powScalar($value);
-        } elseif ($value instanceof Complex) {
+        } elseif ($value instanceof self) {
             return $this->powComplex($value);
         }
 
         throw new \InvalidArgumentException();
     }
 
-    public function powComplex(Complex $value) : Complex
+    public function powComplex(self $value) : self
     {
 
     }
@@ -173,7 +173,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function powInteger(int $value) : Complex
+    public function powInteger(int $value) : self
     {
         if ($value === 0) {
             return new self(1, 0);
@@ -184,7 +184,7 @@ final class Complex
         return $this->multComplex($this->powInteger(--$value));
     }
 
-    public function powScalar($value) : Complex
+    public function powScalar($value) : self
     {
 
     }
@@ -200,11 +200,11 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function add($value) : Complex
+    public function add($value) : self
     {
         if (\is_numeric($value)) {
             return $this->addScalar($value);
-        } elseif ($value instanceof Complex) {
+        } elseif ($value instanceof self) {
             return $this->addComplex($value);
         }
 
@@ -220,7 +220,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function addComplex(Complex $cpl) : Complex
+    private function addComplex(self $cpl) : self
     {
         return new self($this->re + $cpl->re(), $this->im + $cpl->im());
     }
@@ -234,7 +234,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function addScalar($val) : Complex
+    private function addScalar($val) : self
     {
         return new self($this->re + $val, $this->im);
     }
@@ -250,11 +250,11 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function sub($value) : Complex
+    public function sub($value) : self
     {
         if (\is_numeric($value)) {
             return $this->subScalar($value);
-        } elseif ($value instanceof Complex) {
+        } elseif ($value instanceof self) {
             return $this->subComplex($value);
         }
 
@@ -270,7 +270,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function subComplex(Complex $cpl) : Complex
+    private function subComplex(self $cpl) : self
     {
         return new self($this->re - $cpl->re(), $this->im - $cpl->im());
     }
@@ -284,7 +284,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function subScalar($val) : Complex
+    private function subScalar($val) : self
     {
         return new self($this->re - $val, $this->im);
     }
@@ -300,11 +300,11 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function mult($value) : Complex
+    public function mult($value) : self
     {
         if (\is_numeric($value)) {
             return $this->multScalar($value);
-        } elseif ($value instanceof Complex) {
+        } elseif ($value instanceof self) {
             return $this->multComplex($value);
         }
 
@@ -320,7 +320,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function multComplex(Complex $cpl) : Complex
+    private function multComplex(self $cpl) : self
     {
         return new self(
             $this->re * $cpl->re() - $this->im * $cpl->im(),
@@ -337,7 +337,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function multScalar($val) : Complex
+    private function multScalar($val) : self
     {
         return new self($this->re * $val, $this->im * $val);
     }
@@ -353,11 +353,11 @@ final class Complex
      *
      * @since  1.0.0
      */
-    public function div($value) : Complex
+    public function div($value) : self
     {
         if (\is_numeric($value)) {
             return $this->divScalar($value);
-        } elseif ($value instanceof Complex) {
+        } elseif ($value instanceof self) {
             return $this->divComplex($value);
         }
 
@@ -373,7 +373,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function divComplex(Complex $cpl) : Complex
+    private function divComplex(self $cpl) : self
     {
         return new self(
             ($this->re * $cpl->re() + $this->im * $cpl->im()) / ($cpl->re() ** 2 + $cpl->im() ** 2),
@@ -390,7 +390,7 @@ final class Complex
      *
      * @since  1.0.0
      */
-    private function divScalar($val) : Complex
+    private function divScalar($val) : self
     {
         return new self($this->re / $val, $this->im / $val);
     }
diff --git a/Message/Console/Response.php b/Message/Console/Response.php
index 3d1bd84ee..f0052d7ce 100644
--- a/Message/Console/Response.php
+++ b/Message/Console/Response.php
@@ -170,7 +170,7 @@ final class Response extends ResponseAbstract implements RenderableInterface
                     FileLogger::MSG_FULL, [
                         'message' => $e->getMessage(),
                         'line'    => __LINE__,
-                        'file'    => Response::class,
+                        'file'    => self::class,
                     ]
                 );
 
diff --git a/Message/Http/Request.php b/Message/Http/Request.php
index 0424decab..4736b5fc6 100644
--- a/Message/Http/Request.php
+++ b/Message/Http/Request.php
@@ -223,7 +223,7 @@ final class Request extends RequestAbstract
      *
      * @since  1.0.0
      */
-    public static function createFromSuperglobals() : Request
+    public static function createFromSuperglobals() : self
     {
         return new self();
     }
diff --git a/Message/Http/Response.php b/Message/Http/Response.php
index 4d3e247a1..9342636ad 100644
--- a/Message/Http/Response.php
+++ b/Message/Http/Response.php
@@ -184,7 +184,7 @@ final class Response extends ResponseAbstract implements RenderableInterface
                     FileLogger::MSG_FULL, [
                         'message' => $e->getMessage(),
                         'line'    => __LINE__,
-                        'file'    => Response::class,
+                        'file'    => self::class,
                     ]
                 );
 
diff --git a/Stdlib/Base/SmartDateTime.php b/Stdlib/Base/SmartDateTime.php
index 48b7e6c7a..95d87e2e6 100644
--- a/Stdlib/Base/SmartDateTime.php
+++ b/Stdlib/Base/SmartDateTime.php
@@ -53,7 +53,7 @@ class SmartDateTime extends \DateTime
      *
      * @since  1.0.0
      */
-    public static function createFromDateTime(\DateTime $date) : SmartDateTime
+    public static function createFromDateTime(\DateTime $date) : self
     {
         return new self($date->format('Y-m-d H:i:s'), $date->getTimezone());
     }
@@ -70,7 +70,7 @@ class SmartDateTime extends \DateTime
      *
      * @since  1.0.0
      */
-    public function createModify(int $y, int $m = 0, int $d = 0, int $calendar = CAL_GREGORIAN) : SmartDateTime
+    public function createModify(int $y, int $m = 0, int $d = 0, int $calendar = CAL_GREGORIAN) : self
     {
         $dt = clone $this;
         $dt->smartModify($y, $m, $d, $calendar);
@@ -90,7 +90,7 @@ class SmartDateTime extends \DateTime
      *
      * @since  1.0.0
      */
-    public function smartModify(int $y, int $m = 0, int $d = 0, int $calendar = CAL_GREGORIAN) : SmartDateTime
+    public function smartModify(int $y, int $m = 0, int $d = 0, int $calendar = CAL_GREGORIAN) : self
     {
         $yearChange  = (int) floor(((int) $this->format('m') - 1 + $m) / 12);
         $yearChange  = ((int) $this->format('m') - 1 + $m) < 0 && ((int) $this->format('m') - 1 + $m) % 12 === 0 ? $yearChange - 1 : $yearChange;
@@ -125,9 +125,9 @@ class SmartDateTime extends \DateTime
      *
      * @since  1.0.0
      */
-    public function getEndOfMonth() : SmartDateTime
+    public function getEndOfMonth() : self
     {
-        return new SmartDateTime($this->format('Y') . '-' . $this->format('m') . '-' . $this->getDaysOfMonth());
+        return new self($this->format('Y') . '-' . $this->format('m') . '-' . $this->getDaysOfMonth());
     }
 
     /**
@@ -137,9 +137,9 @@ class SmartDateTime extends \DateTime
      *
      * @since  1.0.0
      */
-    public function getStartOfMonth() : SmartDateTime
+    public function getStartOfMonth() : self
     {
-        return new SmartDateTime($this->format('Y') . '-' . $this->format('m') . '-01');
+        return new self($this->format('Y') . '-' . $this->format('m') . '-01');
     }
 
     /**
diff --git a/Stdlib/Graph/BinaryTree.php b/Stdlib/Graph/BinaryTree.php
index 99564fe9c..8b32b48dd 100644
--- a/Stdlib/Graph/BinaryTree.php
+++ b/Stdlib/Graph/BinaryTree.php
@@ -26,7 +26,7 @@ namespace phpOMS\Stdlib\Graph;
  */
 class BinaryTree extends Tree
 {
-    public static function invert($list) : BinaryTree
+    public static function invert($list) : self
     {
         if (empty($list->getNodes())) {
             return $list;
@@ -83,7 +83,7 @@ class BinaryTree extends Tree
      *
      * @since  1.0.0
      */
-    public function setLeft(Node $base, Node $left) : BinaryTree
+    public function setLeft(Node $base, Node $left) : self
     {
         if ($this->getLeft($base) === null) {
             $this->addNodeRelative($base, $left);
diff --git a/Stdlib/Graph/Graph.php b/Stdlib/Graph/Graph.php
index a5dee4aba..1832bead0 100644
--- a/Stdlib/Graph/Graph.php
+++ b/Stdlib/Graph/Graph.php
@@ -49,7 +49,7 @@ class Graph
      *
      * @since  1.0.0
      */
-    public function addNode(Node $node) : Graph
+    public function addNode(Node $node) : self
     {
         $this->nodes[] = $node;
 
@@ -66,7 +66,7 @@ class Graph
      *
      * @since  1.0.0
      */
-    public function addNodeRelative(Node $relative, Node $node) : Graph
+    public function addNodeRelative(Node $relative, Node $node) : self
     {
         $this->edges[] = new Edge($relative, $node);
 
@@ -83,7 +83,7 @@ class Graph
      *
      * @since  1.0.0
      */
-    public function setNode($key, Node $node) : Graph
+    public function setNode($key, Node $node) : self
     {
         $this->nodes[$key] = $node;
 
@@ -99,7 +99,7 @@ class Graph
      *
      * @since  1.0.0
      */
-    public function addEdge(Edge $edge) : Graph
+    public function addEdge(Edge $edge) : self
     {
         $this->edges[] = $edge;
 
diff --git a/Stdlib/Graph/Tree.php b/Stdlib/Graph/Tree.php
index 960420bcf..9defa86db 100644
--- a/Stdlib/Graph/Tree.php
+++ b/Stdlib/Graph/Tree.php
@@ -53,7 +53,7 @@ class Tree extends Graph
      *
      * @since  1.0.0
      */
-    public function addRelativeNode(Node $base, Node $node) : Tree
+    public function addRelativeNode(Node $base, Node $node) : self
     {
         parent::addNode($node);
         parent::addEdge(new Edge($base, $node));
diff --git a/System/File/ContainerInterface.php b/System/File/ContainerInterface.php
index e5887072e..ef05b5487 100644
--- a/System/File/ContainerInterface.php
+++ b/System/File/ContainerInterface.php
@@ -275,7 +275,7 @@ interface ContainerInterface
      *
      * @since  1.0.0
      */
-    public function getParent() : ContainerInterface;
+    public function getParent() : self;
 
     /**
      * Create resource at destination path.
diff --git a/System/File/Ftp/File.php b/System/File/Ftp/File.php
index 6ea9b48ab..32a172621 100644
--- a/System/File/Ftp/File.php
+++ b/System/File/Ftp/File.php
@@ -127,7 +127,7 @@ class File extends FileAbstract implements FileInterface
         $content = '';
         $con     = self::ftpConnect($http);
 
-        if (\ftp_chdir($con, File::dirpath($path)) && \ftp_fget($con, $temp, $path, FTP_BINARY, 0)) {
+        if (\ftp_chdir($con, self::dirpath($path)) && \ftp_fget($con, $temp, $path, FTP_BINARY, 0)) {
             \rewind($temp);
             $content = \stream_get_contents($temp);
         }
diff --git a/System/File/StorageAbstract.php b/System/File/StorageAbstract.php
index 3589a07bc..be3946b0f 100644
--- a/System/File/StorageAbstract.php
+++ b/System/File/StorageAbstract.php
@@ -41,7 +41,7 @@ abstract class StorageAbstract
      *
      * @since  1.0.0
      */
-    abstract public static function getInstance() : StorageAbstract;
+    abstract public static function getInstance() : self;
 
     /**
      * Get the internal class type (directory or file) based on path.
diff --git a/Utils/Git/Git.php b/Utils/Git/Git.php
index ffd3c6e5e..9d0f6b74e 100644
--- a/Utils/Git/Git.php
+++ b/Utils/Git/Git.php
@@ -45,7 +45,7 @@ class Git
     public static function test() : bool
     {
         $pipes    = [];
-        $resource = \proc_open(\escapeshellarg(Git::getBin()), [1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
+        $resource = \proc_open(\escapeshellarg(self::getBin()), [1 => ['pipe', 'w'], 2 => ['pipe', 'w']], $pipes);
 
         $stdout = \stream_get_contents($pipes[1]);
         $stderr = \stream_get_contents($pipes[2]);
diff --git a/Utils/Parser/Php/ArrayParser.php b/Utils/Parser/Php/ArrayParser.php
index 828fff8e6..64f21f9e5 100644
--- a/Utils/Parser/Php/ArrayParser.php
+++ b/Utils/Parser/Php/ArrayParser.php
@@ -64,7 +64,7 @@ class ArrayParser
     public static function parseVariable($value, int $depth = 1) : string
     {
         if (\is_array($value)) {
-            return ArrayParser::serializeArray($value, $depth);
+            return self::serializeArray($value, $depth);
         } elseif (\is_string($value)) {
             return '\'' . \str_replace('\'', '\\\'', $value) . '\'';
         } elseif (\is_bool($value)) {
diff --git a/Utils/TaskSchedule/TaskAbstract.php b/Utils/TaskSchedule/TaskAbstract.php
index c663b81f7..c49b784dc 100644
--- a/Utils/TaskSchedule/TaskAbstract.php
+++ b/Utils/TaskSchedule/TaskAbstract.php
@@ -286,5 +286,5 @@ abstract class TaskAbstract
      *
      * @since 1.0.0
      */
-    abstract public static function createWith(array $jobData) : TaskAbstract;
+    abstract public static function createWith(array $jobData) : self;
 }
diff --git a/tests/Log/FileLoggerTest.php b/tests/Log/FileLoggerTest.php
index 998246aac..7532aa267 100644
--- a/tests/Log/FileLoggerTest.php
+++ b/tests/Log/FileLoggerTest.php
@@ -59,55 +59,55 @@ class FileLoggerTest extends \PHPUnit\Framework\TestCase
         $log->emergency(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->alert(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->critical(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->error(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->warning(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->notice(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->info(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->debug(FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         $log->log(LogLevel::DEBUG, FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
 
         self::assertEquals(1, $log->countLogs()['emergency'] ?? 0);
@@ -127,7 +127,7 @@ class FileLoggerTest extends \PHPUnit\Framework\TestCase
         $log->console(FileLogger::MSG_FULL, true, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
         $ob = ob_get_clean();
         self::assertEquals(1, $log->countLogs()['info'] ?? 0);
@@ -156,7 +156,7 @@ class FileLoggerTest extends \PHPUnit\Framework\TestCase
         $log->log('testException', FileLogger::MSG_FULL, [
             'message' => 'msg',
             'line'    => 11,
-            'file'    => FileLoggerTest::class,
+            'file'    => self::class,
         ]);
     }