diff --git a/src/AST/Expander.php b/src/AST/Expander.php
index b876bb37..62d830ff 100644
--- a/src/AST/Expander.php
+++ b/src/AST/Expander.php
@@ -6,15 +6,12 @@
 
 final class Expander implements Node
 {
-    /**
-     * @var string
-     */
-    private $name;
+    private string $name;
 
     /**
      * @var mixed[]
      */
-    private $arguments;
+    private array $arguments = [];
 
     public function __construct(string $name)
     {
@@ -37,6 +34,9 @@ public function hasArguments() : bool
         return (bool) \count($this->arguments);
     }
 
+    /**
+     * @return mixed[]
+     */
     public function getArguments() : array
     {
         return $this->arguments;
diff --git a/src/AST/Pattern.php b/src/AST/Pattern.php
index c4dadd52..4f0f3f88 100644
--- a/src/AST/Pattern.php
+++ b/src/AST/Pattern.php
@@ -6,15 +6,12 @@
 
 final class Pattern implements Node
 {
-    /**
-     * @var Type
-     */
-    private $type;
+    private Type $type;
 
     /**
      * @var mixed[]
      */
-    private $expanders;
+    private array $expanders = [];
 
     public function __construct(Type $type)
     {
diff --git a/src/AST/Type.php b/src/AST/Type.php
index 5b2ac581..4a9acc83 100644
--- a/src/AST/Type.php
+++ b/src/AST/Type.php
@@ -6,10 +6,7 @@
 
 final class Type implements Node
 {
-    /**
-     * @var string
-     */
-    private $type;
+    private string $type;
 
     public function __construct(string $type)
     {
diff --git a/src/Backtrace/InMemoryBacktrace.php b/src/Backtrace/InMemoryBacktrace.php
index 623703e6..4e0bec8f 100644
--- a/src/Backtrace/InMemoryBacktrace.php
+++ b/src/Backtrace/InMemoryBacktrace.php
@@ -11,9 +11,9 @@
 final class InMemoryBacktrace implements Backtrace
 {
     /**
-     * @var mixed[]
+     * @var string[]
      */
-    private $trace;
+    private array $trace = [];
 
     public function __construct()
     {
@@ -31,7 +31,7 @@ public function matcherCanMatch(string $name, $value, bool $result) : void
             '#%d Matcher %s %s match pattern "%s"',
             $this->entriesCount(),
             $name,
-            $result ? 'can' : 'can\'t',
+            $result ? 'can' : "can't",
             new SingleLineString((string) new StringConverter($value))
         );
     }
@@ -118,6 +118,9 @@ public function isEmpty() : bool
         return \count($this->trace) === 0;
     }
 
+    /**
+     * @return mixed[]
+     */
     public function raw() : array
     {
         return $this->trace;
diff --git a/src/Backtrace/VoidBacktrace.php b/src/Backtrace/VoidBacktrace.php
index b20ed06f..72e19d77 100644
--- a/src/Backtrace/VoidBacktrace.php
+++ b/src/Backtrace/VoidBacktrace.php
@@ -46,6 +46,9 @@ public function isEmpty() : bool
         return true;
     }
 
+    /**
+     * @return mixed[]
+     */
     public function raw() : array
     {
         return [];
diff --git a/src/Exception/UnknownTypeException.php b/src/Exception/UnknownTypeException.php
index cc738ac6..b0ca6c63 100644
--- a/src/Exception/UnknownTypeException.php
+++ b/src/Exception/UnknownTypeException.php
@@ -6,10 +6,7 @@
 
 class UnknownTypeException extends Exception
 {
-    /**
-     * @var string
-     */
-    private $type;
+    private string $type;
 
     public function __construct(string $type)
     {
diff --git a/src/Factory/MatcherFactory.php b/src/Factory/MatcherFactory.php
index 350c85a1..397aca6e 100644
--- a/src/Factory/MatcherFactory.php
+++ b/src/Factory/MatcherFactory.php
@@ -32,7 +32,7 @@ private function buildMatchers(Parser $parser, Backtrace $backtrace) : Matcher\C
         $matchers = [$scalarMatchers];
         $matchers[] = new Matcher\JsonMatcher($arrayMatcher, $backtrace);
 
-        if (\class_exists('LSS\XML2Array')) {
+        if (\class_exists(\LSS\XML2Array::class)) {
             $matchers[] = new Matcher\XmlMatcher($arrayMatcher, $backtrace);
         }
 
diff --git a/src/Lexer.php b/src/Lexer.php
index 63f69f96..1984f637 100644
--- a/src/Lexer.php
+++ b/src/Lexer.php
@@ -8,28 +8,64 @@
 
 final class Lexer extends AbstractLexer
 {
+    /**
+     * @var int
+     */
     public const T_NONE = 1;
 
+    /**
+     * @var int
+     */
     public const T_EXPANDER_NAME = 2;
 
+    /**
+     * @var int
+     */
     public const T_CLOSE_PARENTHESIS = 3;
 
+    /**
+     * @var int
+     */
     public const T_OPEN_CURLY_BRACE    = 4;
 
+    /**
+     * @var int
+     */
     public const T_CLOSE_CURLY_BRACE   = 5;
 
+    /**
+     * @var int
+     */
     public const T_STRING = 6;
 
+    /**
+     * @var int
+     */
     public const T_NUMBER = 7;
 
+    /**
+     * @var int
+     */
     public const T_BOOLEAN = 8;
 
+    /**
+     * @var int
+     */
     public const T_NULL = 9;
 
+    /**
+     * @var int
+     */
     public const T_COMMA  = 10;
 
+    /**
+     * @var int
+     */
     public const T_COLON = 11;
 
+    /**
+     * @var int
+     */
     public const T_TYPE_PATTERN = 12;
 
     /**
@@ -49,6 +85,8 @@ protected function getCatchablePatterns() : array
 
     /**
      * Lexical non-catchable patterns.
+     *
+     * @return string[]
      */
     protected function getNonCatchablePatterns() : array
     {
diff --git a/src/Matcher.php b/src/Matcher.php
index 93db609f..ddf23332 100644
--- a/src/Matcher.php
+++ b/src/Matcher.php
@@ -8,15 +8,9 @@
 
 final class Matcher
 {
-    /**
-     * @var ValueMatcher
-     */
-    private $valueMatcher;
+    private ValueMatcher $valueMatcher;
 
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(ValueMatcher $valueMatcher, Backtrace $backtrace)
     {
diff --git a/src/Matcher/ArrayMatcher.php b/src/Matcher/ArrayMatcher.php
index ea760c23..c2ac7239 100644
--- a/src/Matcher/ArrayMatcher.php
+++ b/src/Matcher/ArrayMatcher.php
@@ -11,26 +11,26 @@
 
 final class ArrayMatcher extends Matcher
 {
-    public const PATTERN = 'array';
-
-    public const UNBOUNDED_PATTERN = '@...@';
-
-    public const UNIVERSAL_KEY = '@*@';
-
     /**
-     * @var ValueMatcher
+     * @var string
      */
-    private $propertyMatcher;
+    public const PATTERN = 'array';
 
     /**
-     * @var Parser
+     * @var string
      */
-    private $parser;
+    public const UNBOUNDED_PATTERN = '@...@';
 
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const UNIVERSAL_KEY = '@*@';
+
+    private ValueMatcher $propertyMatcher;
+
+    private Parser $parser;
+
+    private Backtrace $backtrace;
 
     public function __construct(ValueMatcher $propertyMatcher, Backtrace $backtrace, Parser $parser)
     {
@@ -140,9 +140,7 @@ private function isPatternValid(array $pattern, array $values, string $parentPat
 
         $pattern = \array_filter(
             $pattern,
-            function ($item) use ($skipPattern) {
-                return $item !== $skipPattern;
-            }
+            fn ($item) => $item !== $skipPattern
         );
 
         $notExistingKeys = $this->findNotExistingKeys($pattern, $values);
@@ -158,11 +156,14 @@ function ($item) use ($skipPattern) {
         return true;
     }
 
+    /**
+     * @return mixed[]
+     */
     private function findNotExistingKeys(array $patterns, array $values) : array
     {
         $notExistingKeys = \array_diff_key($patterns, $values);
 
-        return \array_filter($notExistingKeys, function ($pattern, $key) use ($values) {
+        return \array_filter($notExistingKeys, function ($pattern, $key) use ($values) : bool {
             if ($key === self::UNIVERSAL_KEY) {
                 return false;
             }
diff --git a/src/Matcher/BooleanMatcher.php b/src/Matcher/BooleanMatcher.php
index e2af2c2b..39559074 100644
--- a/src/Matcher/BooleanMatcher.php
+++ b/src/Matcher/BooleanMatcher.php
@@ -10,17 +10,14 @@
 
 final class BooleanMatcher extends Matcher
 {
-    public const PATTERN = 'boolean';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN = 'boolean';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/CallbackMatcher.php b/src/Matcher/CallbackMatcher.php
index 2619e18a..b29fe8d2 100644
--- a/src/Matcher/CallbackMatcher.php
+++ b/src/Matcher/CallbackMatcher.php
@@ -9,10 +9,7 @@
 
 final class CallbackMatcher extends Matcher
 {
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
diff --git a/src/Matcher/ChainMatcher.php b/src/Matcher/ChainMatcher.php
index 8a4b484f..b5a1bdb3 100644
--- a/src/Matcher/ChainMatcher.php
+++ b/src/Matcher/ChainMatcher.php
@@ -10,20 +10,14 @@
 
 final class ChainMatcher extends Matcher
 {
-    /**
-     * @var string
-     */
-    private $name;
+    private string $name;
 
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     /**
      * @var ValueMatcher[]
      */
-    private $matchers;
+    private array $matchers = [];
 
     /**
      * @param Backtrace $backtrace
diff --git a/src/Matcher/DateMatcher.php b/src/Matcher/DateMatcher.php
index c7fc9e10..68ab7c0e 100644
--- a/src/Matcher/DateMatcher.php
+++ b/src/Matcher/DateMatcher.php
@@ -11,6 +11,9 @@
 
 final class DateMatcher extends Matcher
 {
+    /**
+     * @var string
+     */
     public const PATTERN = 'date';
 
     private Backtrace $backtrace;
diff --git a/src/Matcher/DateTimeMatcher.php b/src/Matcher/DateTimeMatcher.php
index b9cac4e8..131af4e7 100644
--- a/src/Matcher/DateTimeMatcher.php
+++ b/src/Matcher/DateTimeMatcher.php
@@ -11,6 +11,9 @@
 
 final class DateTimeMatcher extends Matcher
 {
+    /**
+     * @var string
+     */
     public const PATTERN = 'datetime';
 
     private Backtrace $backtrace;
diff --git a/src/Matcher/DoubleMatcher.php b/src/Matcher/DoubleMatcher.php
index ba3755b2..6c5dcba8 100644
--- a/src/Matcher/DoubleMatcher.php
+++ b/src/Matcher/DoubleMatcher.php
@@ -10,17 +10,14 @@
 
 final class DoubleMatcher extends Matcher
 {
-    public const PATTERN = 'double';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN = 'double';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/ExpressionMatcher.php b/src/Matcher/ExpressionMatcher.php
index c7d4c69f..544c506c 100644
--- a/src/Matcher/ExpressionMatcher.php
+++ b/src/Matcher/ExpressionMatcher.php
@@ -10,12 +10,12 @@
 
 final class ExpressionMatcher extends Matcher
 {
-    public const MATCH_PATTERN = "/^expr\((.*?)\)$/";
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const MATCH_PATTERN = "/^expr\((.*?)\)$/";
+
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
diff --git a/src/Matcher/IntegerMatcher.php b/src/Matcher/IntegerMatcher.php
index 1b1389fc..79445565 100644
--- a/src/Matcher/IntegerMatcher.php
+++ b/src/Matcher/IntegerMatcher.php
@@ -10,17 +10,14 @@
 
 final class IntegerMatcher extends Matcher
 {
-    public const PATTERN = 'integer';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN = 'integer';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/JsonMatcher.php b/src/Matcher/JsonMatcher.php
index 4a828890..bd790fcb 100644
--- a/src/Matcher/JsonMatcher.php
+++ b/src/Matcher/JsonMatcher.php
@@ -11,15 +11,9 @@
 
 final class JsonMatcher extends Matcher
 {
-    /**
-     * @var ArrayMatcher
-     */
-    private $arrayMatcher;
-
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private ArrayMatcher $arrayMatcher;
+
+    private Backtrace $backtrace;
 
     public function __construct(ArrayMatcher $arrayMatcher, Backtrace $backtrace)
     {
diff --git a/src/Matcher/JsonObjectMatcher.php b/src/Matcher/JsonObjectMatcher.php
index fa93a400..5bf15439 100644
--- a/src/Matcher/JsonObjectMatcher.php
+++ b/src/Matcher/JsonObjectMatcher.php
@@ -11,17 +11,14 @@
 
 final class JsonObjectMatcher extends Matcher
 {
-    public const JSON_PATTERN = 'json';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const JSON_PATTERN = 'json';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/Matcher.php b/src/Matcher/Matcher.php
index f320785a..f106883d 100644
--- a/src/Matcher/Matcher.php
+++ b/src/Matcher/Matcher.php
@@ -6,10 +6,7 @@
 
 abstract class Matcher implements ValueMatcher
 {
-    /**
-     * @var null|string
-     */
-    protected $error;
+    protected ?string $error = null;
 
     /**
      * @inheritdoc
diff --git a/src/Matcher/NullMatcher.php b/src/Matcher/NullMatcher.php
index a24e462b..eb150d79 100644
--- a/src/Matcher/NullMatcher.php
+++ b/src/Matcher/NullMatcher.php
@@ -9,12 +9,12 @@
 
 final class NullMatcher extends Matcher
 {
-    public const MATCH_PATTERN = '/^@null@$/';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const MATCH_PATTERN = '/^@null@$/';
+
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
diff --git a/src/Matcher/NumberMatcher.php b/src/Matcher/NumberMatcher.php
index 8f6ee39f..9c1474b7 100644
--- a/src/Matcher/NumberMatcher.php
+++ b/src/Matcher/NumberMatcher.php
@@ -10,17 +10,14 @@
 
 final class NumberMatcher extends Matcher
 {
-    public const PATTERN = 'number';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN = 'number';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/OrMatcher.php b/src/Matcher/OrMatcher.php
index f238413b..51cb81e7 100644
--- a/src/Matcher/OrMatcher.php
+++ b/src/Matcher/OrMatcher.php
@@ -8,17 +8,14 @@
 
 final class OrMatcher extends Matcher
 {
-    public const MATCH_PATTERN = "/\|\|/";
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const MATCH_PATTERN = "/\|\|/";
 
-    /**
-     * @var ChainMatcher
-     */
-    private $chainMatcher;
+    private Backtrace $backtrace;
+
+    private ChainMatcher $chainMatcher;
 
     public function __construct(Backtrace $backtrace, ChainMatcher $chainMatcher)
     {
diff --git a/src/Matcher/Pattern/Assert/Json.php b/src/Matcher/Pattern/Assert/Json.php
index d1b5797d..b20053ae 100644
--- a/src/Matcher/Pattern/Assert/Json.php
+++ b/src/Matcher/Pattern/Assert/Json.php
@@ -6,10 +6,19 @@
 
 final class Json
 {
+    /**
+     * @var string
+     */
     private const TRANSFORM_NEW_LINES = '/\r?\n|\r/';
 
+    /**
+     * @var string
+     */
     private const TRANSFORM_QUOTATION_PATTERN = '/([^"])@([a-zA-Z0-9\.]+)@([^"])/';
 
+    /**
+     * @var string
+     */
     private const TRANSFORM_QUOTATION_REPLACEMENT = '$1"@$2@"$3';
 
     public static function isValid($value) : bool
@@ -40,7 +49,7 @@ public static function isValidPattern($value) : bool
         return self::isValid($value) || self::isValid(self::transformPattern($value));
     }
 
-    public static function transformPattern(string $pattern) : string
+    public static function transformPattern(string $pattern) : ?string
     {
         return \preg_replace(
             self::TRANSFORM_NEW_LINES,
diff --git a/src/Matcher/Pattern/Expander/After.php b/src/Matcher/Pattern/Expander/After.php
index e67a37a1..7f13f5f8 100644
--- a/src/Matcher/Pattern/Expander/After.php
+++ b/src/Matcher/Pattern/Expander/After.php
@@ -13,6 +13,9 @@ final class After implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'after';
 
     private ?DateTime $boundaryDateTime;
@@ -33,10 +36,10 @@ public function __construct($boundary)
 
         try {
             $this->boundaryDateTime = DateTime::fromString($boundary);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             try {
                 $this->boundaryTime = Time::fromString($boundary);
-            } catch (\Exception $e) {
+            } catch (\Exception $exception) {
                 throw new \InvalidArgumentException(\sprintf('Boundary value "%s" is not a valid date, date time or time.', new StringConverter($boundary)));
             }
         }
diff --git a/src/Matcher/Pattern/Expander/BacktraceBehavior.php b/src/Matcher/Pattern/Expander/BacktraceBehavior.php
index dcd18145..ee001d0b 100644
--- a/src/Matcher/Pattern/Expander/BacktraceBehavior.php
+++ b/src/Matcher/Pattern/Expander/BacktraceBehavior.php
@@ -8,10 +8,7 @@
 
 trait BacktraceBehavior
 {
-    /**
-     * @var Backtrace
-     */
-    protected $backtrace;
+    protected Backtrace $backtrace;
 
     public function setBacktrace(Backtrace $backtrace) : void
     {
diff --git a/src/Matcher/Pattern/Expander/Before.php b/src/Matcher/Pattern/Expander/Before.php
index 13e5e002..326be32c 100644
--- a/src/Matcher/Pattern/Expander/Before.php
+++ b/src/Matcher/Pattern/Expander/Before.php
@@ -13,6 +13,9 @@ final class Before implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'before';
 
     private ?DateTime $boundaryDateTime;
@@ -33,10 +36,10 @@ public function __construct(string $boundary)
 
         try {
             $this->boundaryDateTime = DateTime::fromString($boundary);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             try {
                 $this->boundaryTime = Time::fromString($boundary);
-            } catch (\Exception $e) {
+            } catch (\Exception $exception) {
                 throw new \InvalidArgumentException(\sprintf('Boundary value "%s" is not a valid date, date time or time.', new StringConverter($boundary)));
             }
         }
diff --git a/src/Matcher/Pattern/Expander/Contains.php b/src/Matcher/Pattern/Expander/Contains.php
index 9834527a..00400aee 100644
--- a/src/Matcher/Pattern/Expander/Contains.php
+++ b/src/Matcher/Pattern/Expander/Contains.php
@@ -11,21 +11,18 @@ final class Contains implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'contains';
-
-    /**
-     * @var null|string
-     */
-    private $error;
-
     /**
      * @var string
      */
-    private $string;
+    public const NAME = 'contains';
+
+    private ?string $error = null;
+
+    private string $string;
 
-    private $ignoreCase;
+    private bool $ignoreCase;
 
-    public function __construct(string $string, $ignoreCase = false)
+    public function __construct(string $string, bool $ignoreCase = false)
     {
         $this->string = $string;
         $this->ignoreCase = $ignoreCase;
diff --git a/src/Matcher/Pattern/Expander/Count.php b/src/Matcher/Pattern/Expander/Count.php
index f6d47f38..8171d98b 100644
--- a/src/Matcher/Pattern/Expander/Count.php
+++ b/src/Matcher/Pattern/Expander/Count.php
@@ -12,17 +12,14 @@ final class Count implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'count';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'count';
 
-    /**
-     * @var int
-     */
-    private $value;
+    private ?string $error = null;
+
+    private int $value;
 
     public function __construct(int $value)
     {
diff --git a/src/Matcher/Pattern/Expander/EndsWith.php b/src/Matcher/Pattern/Expander/EndsWith.php
index 8d98e5dc..ce8ce8a3 100644
--- a/src/Matcher/Pattern/Expander/EndsWith.php
+++ b/src/Matcher/Pattern/Expander/EndsWith.php
@@ -11,22 +11,16 @@ final class EndsWith implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'endsWith';
-
     /**
      * @var string
      */
-    private $stringEnding;
+    public const NAME = 'endsWith';
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private string $stringEnding;
 
-    /**
-     * @var bool
-     */
-    private $ignoreCase;
+    private ?string $error = null;
+
+    private bool $ignoreCase;
 
     public function __construct(string $stringEnding, bool $ignoreCase = false)
     {
diff --git a/src/Matcher/Pattern/Expander/ExpanderMatch.php b/src/Matcher/Pattern/Expander/ExpanderMatch.php
index b26d20df..559a0b0d 100644
--- a/src/Matcher/Pattern/Expander/ExpanderMatch.php
+++ b/src/Matcher/Pattern/Expander/ExpanderMatch.php
@@ -11,20 +11,20 @@ final class ExpanderMatch implements Matcher\Pattern\PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'match';
-
     /**
-     * @var Matcher
+     * @var string
      */
-    private $matcher;
+    public const NAME = 'match';
+
+    private ?Matcher $matcher = null;
 
     /**
-     * @var null|string
+     * @var null|array|string
      */
     private $pattern;
 
     /**
-     * @param null|string $pattern
+     * @param null|array|string $pattern
      */
     public function __construct($pattern)
     {
diff --git a/src/Matcher/Pattern/Expander/GreaterThan.php b/src/Matcher/Pattern/Expander/GreaterThan.php
index 0f81bbcf..74061a26 100644
--- a/src/Matcher/Pattern/Expander/GreaterThan.php
+++ b/src/Matcher/Pattern/Expander/GreaterThan.php
@@ -11,6 +11,9 @@ final class GreaterThan implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'greaterThan';
 
     /**
@@ -18,10 +21,7 @@ final class GreaterThan implements PatternExpander
      */
     private $boundary;
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private ?string $error = null;
 
     public function __construct($boundary)
     {
diff --git a/src/Matcher/Pattern/Expander/HasProperty.php b/src/Matcher/Pattern/Expander/HasProperty.php
index 36f11728..049e5804 100644
--- a/src/Matcher/Pattern/Expander/HasProperty.php
+++ b/src/Matcher/Pattern/Expander/HasProperty.php
@@ -12,16 +12,16 @@ final class HasProperty implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'hasProperty';
 
-    private $propertyName;
+    private string $propertyName;
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private ?string $error = null;
 
-    public function __construct($propertyName)
+    public function __construct(string $propertyName)
     {
         $this->propertyName = $propertyName;
     }
diff --git a/src/Matcher/Pattern/Expander/InArray.php b/src/Matcher/Pattern/Expander/InArray.php
index 51aed569..d4bebd02 100644
--- a/src/Matcher/Pattern/Expander/InArray.php
+++ b/src/Matcher/Pattern/Expander/InArray.php
@@ -11,12 +11,12 @@ final class InArray implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'inArray';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'inArray';
+
+    private ?string $error = null;
 
     private $value;
 
diff --git a/src/Matcher/Pattern/Expander/IsDateTime.php b/src/Matcher/Pattern/Expander/IsDateTime.php
index a4e9b2c5..307b0bba 100644
--- a/src/Matcher/Pattern/Expander/IsDateTime.php
+++ b/src/Matcher/Pattern/Expander/IsDateTime.php
@@ -11,12 +11,12 @@ final class IsDateTime implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isDateTime';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isDateTime';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
@@ -57,7 +57,7 @@ private function matchValue(string $value) : bool
             new \DateTime($value);
 
             return true;
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             return false;
         }
     }
diff --git a/src/Matcher/Pattern/Expander/IsEmail.php b/src/Matcher/Pattern/Expander/IsEmail.php
index 6509bd78..eeac52f0 100644
--- a/src/Matcher/Pattern/Expander/IsEmail.php
+++ b/src/Matcher/Pattern/Expander/IsEmail.php
@@ -11,12 +11,12 @@ final class IsEmail implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isEmail';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isEmail';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
@@ -55,7 +55,7 @@ private function matchValue(string $value) : bool
     {
         try {
             return false !== \filter_var($value, FILTER_VALIDATE_EMAIL);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             return false;
         }
     }
diff --git a/src/Matcher/Pattern/Expander/IsEmpty.php b/src/Matcher/Pattern/Expander/IsEmpty.php
index e9e2bceb..06b2eed6 100644
--- a/src/Matcher/Pattern/Expander/IsEmpty.php
+++ b/src/Matcher/Pattern/Expander/IsEmpty.php
@@ -11,12 +11,12 @@ final class IsEmpty implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isEmpty';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isEmpty';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
diff --git a/src/Matcher/Pattern/Expander/IsIp.php b/src/Matcher/Pattern/Expander/IsIp.php
index 3e294275..09e5a5f4 100644
--- a/src/Matcher/Pattern/Expander/IsIp.php
+++ b/src/Matcher/Pattern/Expander/IsIp.php
@@ -11,12 +11,12 @@ final class IsIp implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isIp';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isIp';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
@@ -55,7 +55,7 @@ private function matchValue(string $value) : bool
     {
         try {
             return false !== \filter_var($value, FILTER_VALIDATE_IP);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             return false;
         }
     }
diff --git a/src/Matcher/Pattern/Expander/IsNotEmpty.php b/src/Matcher/Pattern/Expander/IsNotEmpty.php
index 52d8dc9c..86d0269b 100644
--- a/src/Matcher/Pattern/Expander/IsNotEmpty.php
+++ b/src/Matcher/Pattern/Expander/IsNotEmpty.php
@@ -11,12 +11,12 @@ final class IsNotEmpty implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isNotEmpty';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isNotEmpty';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
diff --git a/src/Matcher/Pattern/Expander/IsTzAbbreviation.php b/src/Matcher/Pattern/Expander/IsTzAbbreviation.php
index 24cc4b1e..3fdd73b3 100644
--- a/src/Matcher/Pattern/Expander/IsTzAbbreviation.php
+++ b/src/Matcher/Pattern/Expander/IsTzAbbreviation.php
@@ -12,6 +12,9 @@ final class IsTzAbbreviation implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'isTzAbbreviation';
 
     private ?string $error;
@@ -48,7 +51,7 @@ public function match($value) : bool
             }
 
             return $result;
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             $this->error = \sprintf('Timezone expander require valid timezone, got "%s".', new StringConverter($value));
             $this->backtrace->expanderFailed(self::NAME, $value, $this->error);
 
diff --git a/src/Matcher/Pattern/Expander/IsTzIdentifier.php b/src/Matcher/Pattern/Expander/IsTzIdentifier.php
index 1c186588..d78911c7 100644
--- a/src/Matcher/Pattern/Expander/IsTzIdentifier.php
+++ b/src/Matcher/Pattern/Expander/IsTzIdentifier.php
@@ -12,6 +12,9 @@ final class IsTzIdentifier implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'isTzIdentifier';
 
     private ?string $error;
@@ -48,7 +51,7 @@ public function match($value) : bool
             }
 
             return $result;
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             $this->error = \sprintf('Timezone expander require valid timezone, got "%s".', new StringConverter($value));
             $this->backtrace->expanderFailed(self::NAME, $value, $this->error);
 
diff --git a/src/Matcher/Pattern/Expander/IsTzOffset.php b/src/Matcher/Pattern/Expander/IsTzOffset.php
index f1e275a5..5f1bc750 100644
--- a/src/Matcher/Pattern/Expander/IsTzOffset.php
+++ b/src/Matcher/Pattern/Expander/IsTzOffset.php
@@ -12,6 +12,9 @@ final class IsTzOffset implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'isTzOffset';
 
     private ?string $error;
@@ -48,7 +51,7 @@ public function match($value) : bool
             }
 
             return $result;
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             $this->error = \sprintf('Timezone expander require valid timezone, got "%s".', new StringConverter($value));
             $this->backtrace->expanderFailed(self::NAME, $value, $this->error);
 
diff --git a/src/Matcher/Pattern/Expander/IsUrl.php b/src/Matcher/Pattern/Expander/IsUrl.php
index be5f0724..94c846bc 100644
--- a/src/Matcher/Pattern/Expander/IsUrl.php
+++ b/src/Matcher/Pattern/Expander/IsUrl.php
@@ -11,12 +11,12 @@ final class IsUrl implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'isUrl';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'isUrl';
+
+    private ?string $error = null;
 
     public static function is(string $name) : bool
     {
@@ -55,7 +55,7 @@ private function matchValue(string $value) : bool
     {
         try {
             return false !== \filter_var($value, FILTER_VALIDATE_URL);
-        } catch (\Exception $e) {
+        } catch (\Exception $exception) {
             return false;
         }
     }
diff --git a/src/Matcher/Pattern/Expander/LowerThan.php b/src/Matcher/Pattern/Expander/LowerThan.php
index 59c3a746..397c5335 100644
--- a/src/Matcher/Pattern/Expander/LowerThan.php
+++ b/src/Matcher/Pattern/Expander/LowerThan.php
@@ -11,6 +11,9 @@ final class LowerThan implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'lowerThan';
 
     /**
@@ -18,10 +21,7 @@ final class LowerThan implements PatternExpander
      */
     private $boundary;
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private ?string $error = null;
 
     public function __construct($boundary)
     {
diff --git a/src/Matcher/Pattern/Expander/MatchRegex.php b/src/Matcher/Pattern/Expander/MatchRegex.php
index 5e68effa..d613ca80 100644
--- a/src/Matcher/Pattern/Expander/MatchRegex.php
+++ b/src/Matcher/Pattern/Expander/MatchRegex.php
@@ -11,17 +11,14 @@ final class MatchRegex implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'matchRegex';
-
-    /**
-     * @var null|string
-     */
-    private $error;
-
     /**
      * @var string
      */
-    private $pattern;
+    public const NAME = 'matchRegex';
+
+    private ?string $error = null;
+
+    private string $pattern;
 
     public function __construct(string $pattern)
     {
diff --git a/src/Matcher/Pattern/Expander/NotContains.php b/src/Matcher/Pattern/Expander/NotContains.php
index a2eb9547..daf9fdc8 100644
--- a/src/Matcher/Pattern/Expander/NotContains.php
+++ b/src/Matcher/Pattern/Expander/NotContains.php
@@ -11,17 +11,14 @@ final class NotContains implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'notContains';
-
-    /**
-     * @var null|string
-     */
-    private $error;
-
     /**
      * @var string
      */
-    private $string;
+    public const NAME = 'notContains';
+
+    private ?string $error = null;
+
+    private string $string;
 
     private $ignoreCase;
 
diff --git a/src/Matcher/Pattern/Expander/OneOf.php b/src/Matcher/Pattern/Expander/OneOf.php
index 503c11ed..c8f6ed70 100644
--- a/src/Matcher/Pattern/Expander/OneOf.php
+++ b/src/Matcher/Pattern/Expander/OneOf.php
@@ -11,17 +11,17 @@ final class OneOf implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'oneOf';
 
     /**
      * @var PatternExpander[]
      */
-    private $expanders;
+    private ?array $expanders = null;
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private ?string $error = null;
 
     public function __construct()
     {
diff --git a/src/Matcher/Pattern/Expander/Optional.php b/src/Matcher/Pattern/Expander/Optional.php
index b2ec41bd..d18e05d3 100644
--- a/src/Matcher/Pattern/Expander/Optional.php
+++ b/src/Matcher/Pattern/Expander/Optional.php
@@ -10,6 +10,9 @@ final class Optional implements PatternExpander
 {
     use BacktraceBehavior;
 
+    /**
+     * @var string
+     */
     public const NAME = 'optional';
 
     public static function is(string $name) : bool
diff --git a/src/Matcher/Pattern/Expander/Repeat.php b/src/Matcher/Pattern/Expander/Repeat.php
index 730d9d2a..4334736c 100644
--- a/src/Matcher/Pattern/Expander/Repeat.php
+++ b/src/Matcher/Pattern/Expander/Repeat.php
@@ -13,27 +13,21 @@ final class Repeat implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'repeat';
-
     /**
-     * @var null|string
+     * @var string
      */
-    private $error;
+    public const NAME = 'repeat';
+
+    private ?string $error = null;
 
     /**
      * @var mixed[]|string
      */
     private $pattern;
 
-    /**
-     * @var bool
-     */
-    private $isStrict;
+    private bool $isStrict;
 
-    /**
-     * @var bool
-     */
-    private $isScalar;
+    private bool $isScalar;
 
     /**
      * @param array|string $pattern array to be matched or json-encoded string
diff --git a/src/Matcher/Pattern/Expander/StartsWith.php b/src/Matcher/Pattern/Expander/StartsWith.php
index 0be7aaff..3ddd99e7 100644
--- a/src/Matcher/Pattern/Expander/StartsWith.php
+++ b/src/Matcher/Pattern/Expander/StartsWith.php
@@ -11,22 +11,16 @@ final class StartsWith implements PatternExpander
 {
     use BacktraceBehavior;
 
-    public const NAME = 'startsWith';
-
     /**
      * @var string
      */
-    private $stringBeginning;
+    public const NAME = 'startsWith';
 
-    /**
-     * @var null|string
-     */
-    private $error;
+    private string $stringBeginning;
 
-    /**
-     * @var bool
-     */
-    private $ignoreCase;
+    private ?string $error = null;
+
+    private bool $ignoreCase;
 
     public function __construct(string $stringBeginning, bool $ignoreCase = false)
     {
diff --git a/src/Matcher/Pattern/Pattern.php b/src/Matcher/Pattern/Pattern.php
index 409ecc6f..4fe8da7f 100644
--- a/src/Matcher/Pattern/Pattern.php
+++ b/src/Matcher/Pattern/Pattern.php
@@ -10,7 +10,7 @@ public function addExpander(PatternExpander $expander);
 
     public function matchExpanders($value) : bool;
 
-    public function getError();
+    public function getError() : ?string;
 
     public function hasExpander(string $expanderName) : bool;
 }
diff --git a/src/Matcher/Pattern/TypePattern.php b/src/Matcher/Pattern/TypePattern.php
index e6dad37e..cf59112e 100644
--- a/src/Matcher/Pattern/TypePattern.php
+++ b/src/Matcher/Pattern/TypePattern.php
@@ -6,17 +6,14 @@
 
 final class TypePattern implements Pattern
 {
-    /**
-     * @var string
-     */
-    private $type;
+    private string $type;
 
     /**
      * @var PatternExpander[]
      */
-    private $expanders;
+    private array $expanders = [];
 
-    private $error;
+    private ?string $error = null;
 
     public function __construct(string $type)
     {
@@ -52,7 +49,7 @@ public function matchExpanders($value) : bool
         return true;
     }
 
-    public function getError()
+    public function getError() : ?string
     {
         return $this->error;
     }
diff --git a/src/Matcher/ScalarMatcher.php b/src/Matcher/ScalarMatcher.php
index 76d8435f..ae49e6a1 100644
--- a/src/Matcher/ScalarMatcher.php
+++ b/src/Matcher/ScalarMatcher.php
@@ -10,10 +10,7 @@
 
 final class ScalarMatcher extends Matcher
 {
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
diff --git a/src/Matcher/StringMatcher.php b/src/Matcher/StringMatcher.php
index 6e9d8ca1..fd7e26f1 100644
--- a/src/Matcher/StringMatcher.php
+++ b/src/Matcher/StringMatcher.php
@@ -10,17 +10,14 @@
 
 final class StringMatcher extends Matcher
 {
-    public const PATTERN = 'string';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN = 'string';
 
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/TextMatcher.php b/src/Matcher/TextMatcher.php
index 1cb2bef9..1cba09df 100644
--- a/src/Matcher/TextMatcher.php
+++ b/src/Matcher/TextMatcher.php
@@ -16,24 +16,21 @@
 
 final class TextMatcher extends Matcher
 {
-    public const PATTERN_REGEXP = "/@[a-zA-Z\\.]+@(\\.\\w+\\([a-zA-Z0-9{},:@\\.\"'\\(\\)]*\\))*/";
-
-    public const PATTERN_REGEXP_PLACEHOLDER_TEMPLATE = '__PLACEHOLDER%d__';
-
     /**
-     * @var Parser
+     * @var string
      */
-    private $parser;
+    public const PATTERN_REGEXP = "/@[a-zA-Z\\.]+@(\\.\\w+\\([a-zA-Z0-9{},:@\\.\"'\\(\\)]*\\))*/";
 
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const PATTERN_REGEXP_PLACEHOLDER_TEMPLATE = '__PLACEHOLDER%d__';
 
-    /**
-     * @var ValueMatcher
-     */
-    private $matcher;
+    private Parser $parser;
+
+    private Backtrace $backtrace;
+
+    private ValueMatcher $matcher;
 
     public function __construct(ValueMatcher $matcher, Backtrace $backtrace, Parser $parser)
     {
@@ -62,8 +59,8 @@ public function match($value, $pattern) : bool
 
         try {
             $patternRegex = $this->replacePlaceholderWithPatternRegexes($patternRegex, $patternsReplacedWithRegex);
-        } catch (UnknownTypeException $exception) {
-            $this->error = \sprintf('Type pattern "%s" is not supported by TextMatcher.', $exception->getType());
+        } catch (UnknownTypeException $unknownTypeException) {
+            $this->error = \sprintf('Type pattern "%s" is not supported by TextMatcher.', $unknownTypeException->getType());
             $this->backtrace->matcherFailed(self::class, $value, $pattern, (string) $this->error);
 
             return false;
diff --git a/src/Matcher/TimeMatcher.php b/src/Matcher/TimeMatcher.php
index 22bc857b..0f78cfdb 100644
--- a/src/Matcher/TimeMatcher.php
+++ b/src/Matcher/TimeMatcher.php
@@ -11,6 +11,9 @@
 
 final class TimeMatcher extends Matcher
 {
+    /**
+     * @var string
+     */
     public const PATTERN = 'time';
 
     private Backtrace $backtrace;
diff --git a/src/Matcher/TimeZoneMatcher.php b/src/Matcher/TimeZoneMatcher.php
index 04cf2272..170dfcb2 100644
--- a/src/Matcher/TimeZoneMatcher.php
+++ b/src/Matcher/TimeZoneMatcher.php
@@ -11,8 +11,14 @@
 
 final class TimeZoneMatcher extends Matcher
 {
+    /**
+     * @var string
+     */
     public const PATTERN = 'timezone';
 
+    /**
+     * @var string
+     */
     public const PATTERN_SHORT = 'tz';
 
     private Backtrace $backtrace;
diff --git a/src/Matcher/UuidMatcher.php b/src/Matcher/UuidMatcher.php
index 27976f30..37c608f2 100644
--- a/src/Matcher/UuidMatcher.php
+++ b/src/Matcher/UuidMatcher.php
@@ -10,21 +10,24 @@
 
 final class UuidMatcher extends Matcher
 {
+    /**
+     * @var string
+     */
     public const PATTERN = 'uuid';
 
-    public const UUID_PATTERN = '[\da-f]{8}-[\da-f]{4}-[1-5][\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}';
-
-    public const UUID_FORMAT_PATTERN = '|^' . self::UUID_PATTERN . '$|';
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const UUID_PATTERN = '[\da-f]{8}-[\da-f]{4}-[1-5][\da-f]{3}-[89ab][\da-f]{3}-[\da-f]{12}';
 
     /**
-     * @var Parser
+     * @var string
      */
-    private $parser;
+    public const UUID_FORMAT_PATTERN = '|^' . self::UUID_PATTERN . '$|';
+
+    private Backtrace $backtrace;
+
+    private Parser $parser;
 
     public function __construct(Backtrace $backtrace, Parser $parser)
     {
diff --git a/src/Matcher/WildcardMatcher.php b/src/Matcher/WildcardMatcher.php
index 3f59d300..ce659524 100644
--- a/src/Matcher/WildcardMatcher.php
+++ b/src/Matcher/WildcardMatcher.php
@@ -8,12 +8,12 @@
 
 final class WildcardMatcher extends Matcher
 {
-    public const MATCH_PATTERN = "/^@(\*|wildcard)@$/";
-
     /**
-     * @var Backtrace
+     * @var string
      */
-    private $backtrace;
+    public const MATCH_PATTERN = "/^@(\*|wildcard)@$/";
+
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
diff --git a/src/Matcher/XmlMatcher.php b/src/Matcher/XmlMatcher.php
index a6af10b5..476b8b79 100644
--- a/src/Matcher/XmlMatcher.php
+++ b/src/Matcher/XmlMatcher.php
@@ -11,15 +11,9 @@
 
 final class XmlMatcher extends Matcher
 {
-    /**
-     * @var ArrayMatcher
-     */
-    private $arrayMatcher;
+    private ArrayMatcher $arrayMatcher;
 
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(ArrayMatcher $arrayMatcher, Backtrace $backtrace)
     {
@@ -38,7 +32,7 @@ public function match($value, $pattern) : bool
         }
 
         if (!Xml::isValid($value) || !Xml::isValid($pattern)) {
-            $this->error = \sprintf('Value or pattern are not valid XML\'s');
+            $this->error = \sprintf("Value or pattern are not valid XML's");
             $this->backtrace->matcherFailed(self::class, $value, $pattern, $this->error);
 
             return false;
diff --git a/src/PHPMatcher.php b/src/PHPMatcher.php
index 3638c2bb..f77d571f 100644
--- a/src/PHPMatcher.php
+++ b/src/PHPMatcher.php
@@ -9,15 +9,9 @@
 
 final class PHPMatcher
 {
-    /**
-     * @var null|Matcher
-     */
-    private $matcher;
+    private ?Matcher $matcher = null;
 
-    /**
-     * @var Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(?Backtrace $backtrace = null)
     {
diff --git a/src/PHPUnit/PHPMatcherAssertions.php b/src/PHPUnit/PHPMatcherAssertions.php
index b9fbb90e..f884f91d 100644
--- a/src/PHPUnit/PHPMatcherAssertions.php
+++ b/src/PHPUnit/PHPMatcherAssertions.php
@@ -9,10 +9,7 @@
 
 trait PHPMatcherAssertions
 {
-    /**
-     * @var null|Backtrace
-     */
-    protected $backtrace;
+    protected ?Backtrace $backtrace = null;
 
     protected function setBacktrace(Backtrace $backtrace) : void
     {
diff --git a/src/PHPUnit/PHPMatcherConstraint.php b/src/PHPUnit/PHPMatcherConstraint.php
index d27005ee..15f02f3d 100644
--- a/src/PHPUnit/PHPMatcherConstraint.php
+++ b/src/PHPUnit/PHPMatcherConstraint.php
@@ -14,10 +14,7 @@ final class PHPMatcherConstraint extends Constraint
 {
     private $pattern;
 
-    /**
-     * @var PHPMatcher
-     */
-    private $matcher;
+    private PHPMatcher $matcher;
 
     private $lastValue;
 
diff --git a/src/Parser.php b/src/Parser.php
index d8a5016a..878e1634 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -11,17 +11,14 @@
 
 final class Parser
 {
-    public const NULL_VALUE = 'null';
-
     /**
-     * @var Lexer
+     * @var string
      */
-    private $lexer;
+    public const NULL_VALUE = 'null';
 
-    /**
-     * @var ExpanderInitializer
-     */
-    private $expanderInitializer;
+    private Lexer $lexer;
+
+    private ExpanderInitializer $expanderInitializer;
 
     public function __construct(Lexer $lexer, ExpanderInitializer $expanderInitializer)
     {
@@ -35,7 +32,7 @@ public function hasValidSyntax(string $pattern) : bool
             $this->getAST($pattern);
 
             return true;
-        } catch (Exception $e) {
+        } catch (Exception $exception) {
             return false;
         }
     }
@@ -69,14 +66,10 @@ private function getPattern() : AST\Pattern
 
         $pattern = null;
 
-        switch ($this->lexer->lookahead['type']) {
-            case Lexer::T_TYPE_PATTERN:
-                $pattern = new AST\Pattern(new AST\Type($this->lexer->lookahead['value']));
-
-                break;
-
-            default:
-                throw PatternException::syntaxError($this->unexpectedSyntaxError($this->lexer->lookahead, '@type@ pattern'));
+        if ($this->lexer->lookahead['type'] == Lexer::T_TYPE_PATTERN) {
+            $pattern = new AST\Pattern(new AST\Type($this->lexer->lookahead['value']));
+        } else {
+            throw PatternException::syntaxError($this->unexpectedSyntaxError($this->lexer->lookahead, '@type@ pattern'));
         }
 
         $this->lexer->moveNext();
@@ -218,10 +211,10 @@ private function getArrayArgument() : array
         return $arrayArgument;
     }
 
-    private function getNextArrayElement(array &$array)
+    private function getNextArrayElement(array &$array) : ?bool
     {
         if ($this->lexer->isNextToken(Lexer::T_CLOSE_CURLY_BRACE)) {
-            return;
+            return null;
         }
 
         $key = $this->getNextArgumentValue();
@@ -245,7 +238,7 @@ private function getNextArrayElement(array &$array)
         $array[$key] = $value;
 
         if (!$this->lexer->isNextToken(Lexer::T_COMMA)) {
-            return;
+            return null;
         }
 
         return true;
diff --git a/src/Parser/ExpanderInitializer.php b/src/Parser/ExpanderInitializer.php
index edd98e2e..ff6d0986 100644
--- a/src/Parser/ExpanderInitializer.php
+++ b/src/Parser/ExpanderInitializer.php
@@ -4,13 +4,13 @@
 
 namespace Coduo\PHPMatcher\Parser;
 
-use Coduo\PHPMatcher\AST\Expander as ExpanderNode;
+use Coduo\PHPMatcher\AST\Expander;
 use Coduo\PHPMatcher\Backtrace;
 use Coduo\PHPMatcher\Exception\InvalidArgumentException;
 use Coduo\PHPMatcher\Exception\InvalidExpanderTypeException;
 use Coduo\PHPMatcher\Exception\UnknownExpanderClassException;
 use Coduo\PHPMatcher\Exception\UnknownExpanderException;
-use Coduo\PHPMatcher\Matcher\Pattern\Expander;
+use Coduo\PHPMatcher\Matcher\Pattern;
 use Coduo\PHPMatcher\Matcher\Pattern\PatternExpander;
 
 final class ExpanderInitializer
@@ -18,38 +18,35 @@ final class ExpanderInitializer
     /**
      * @var class-string[]
      */
-    private $expanderDefinitions = [
-        Expander\After::NAME => Expander\After::class,
-        Expander\Before::NAME => Expander\Before::class,
-        Expander\Contains::NAME => Expander\Contains::class,
-        Expander\NotContains::NAME => Expander\NotContains::class,
-        Expander\Count::NAME => Expander\Count::class,
-        Expander\EndsWith::NAME => Expander\EndsWith::class,
-        Expander\GreaterThan::NAME => Expander\GreaterThan::class,
-        Expander\InArray::NAME => Expander\InArray::class,
-        Expander\IsDateTime::NAME => Expander\IsDateTime::class,
-        Expander\IsEmail::NAME => Expander\IsEmail::class,
-        Expander\IsEmpty::NAME => Expander\IsEmpty::class,
-        Expander\IsNotEmpty::NAME => Expander\IsNotEmpty::class,
-        Expander\IsUrl::NAME => Expander\IsUrl::class,
-        Expander\IsIp::NAME => Expander\IsIp::class,
-        Expander\IsTzOffset::NAME => Expander\IsTzOffset::class,
-        Expander\IsTzAbbreviation::NAME => Expander\IsTzAbbreviation::class,
-        Expander\IsTzIdentifier::NAME => Expander\IsTzIdentifier::class,
-        Expander\LowerThan::NAME => Expander\LowerThan::class,
-        Expander\MatchRegex::NAME => Expander\MatchRegex::class,
-        Expander\OneOf::NAME => Expander\OneOf::class,
-        Expander\Optional::NAME => Expander\Optional::class,
-        Expander\StartsWith::NAME => Expander\StartsWith::class,
-        Expander\Repeat::NAME => Expander\Repeat::class,
-        Expander\ExpanderMatch::NAME => Expander\ExpanderMatch::class,
-        Expander\HasProperty::NAME => Expander\HasProperty::class,
+    private array $expanderDefinitions = [
+        Pattern\Expander\After::NAME => Pattern\Expander\After::class,
+        Pattern\Expander\Before::NAME => Pattern\Expander\Before::class,
+        Pattern\Expander\Contains::NAME => Pattern\Expander\Contains::class,
+        Pattern\Expander\NotContains::NAME => Pattern\Expander\NotContains::class,
+        Pattern\Expander\Count::NAME => Pattern\Expander\Count::class,
+        Pattern\Expander\EndsWith::NAME => Pattern\Expander\EndsWith::class,
+        Pattern\Expander\GreaterThan::NAME => Pattern\Expander\GreaterThan::class,
+        Pattern\Expander\InArray::NAME => Pattern\Expander\InArray::class,
+        Pattern\Expander\IsDateTime::NAME => Pattern\Expander\IsDateTime::class,
+        Pattern\Expander\IsEmail::NAME => Pattern\Expander\IsEmail::class,
+        Pattern\Expander\IsEmpty::NAME => Pattern\Expander\IsEmpty::class,
+        Pattern\Expander\IsNotEmpty::NAME => Pattern\Expander\IsNotEmpty::class,
+        Pattern\Expander\IsUrl::NAME => Pattern\Expander\IsUrl::class,
+        Pattern\Expander\IsIp::NAME => Pattern\Expander\IsIp::class,
+        Pattern\Expander\IsTzOffset::NAME => Pattern\Expander\IsTzOffset::class,
+        Pattern\Expander\IsTzAbbreviation::NAME => Pattern\Expander\IsTzAbbreviation::class,
+        Pattern\Expander\IsTzIdentifier::NAME => Pattern\Expander\IsTzIdentifier::class,
+        Pattern\Expander\LowerThan::NAME => Pattern\Expander\LowerThan::class,
+        Pattern\Expander\MatchRegex::NAME => Pattern\Expander\MatchRegex::class,
+        Pattern\Expander\OneOf::NAME => Pattern\Expander\OneOf::class,
+        Pattern\Expander\Optional::NAME => Pattern\Expander\Optional::class,
+        Pattern\Expander\StartsWith::NAME => Pattern\Expander\StartsWith::class,
+        Pattern\Expander\Repeat::NAME => Pattern\Expander\Repeat::class,
+        Pattern\Expander\ExpanderMatch::NAME => Pattern\Expander\ExpanderMatch::class,
+        Pattern\Expander\HasProperty::NAME => Pattern\Expander\HasProperty::class,
     ];
 
-    /**
-     * @var \Coduo\PHPMatcher\Backtrace
-     */
-    private $backtrace;
+    private Backtrace $backtrace;
 
     public function __construct(Backtrace $backtrace)
     {
@@ -79,7 +76,7 @@ public function getExpanderDefinition(string $expanderName) : string
         return $this->expanderDefinitions[$expanderName];
     }
 
-    public function initialize(ExpanderNode $expanderNode) : PatternExpander
+    public function initialize(Expander $expanderNode) : PatternExpander
     {
         if (!\array_key_exists($expanderNode->getName(), $this->expanderDefinitions)) {
             throw new UnknownExpanderException(\sprintf('Unknown expander "%s"', $expanderNode->getName()));
@@ -91,7 +88,7 @@ public function initialize(ExpanderNode $expanderNode) : PatternExpander
             $arguments = [];
 
             foreach ($expanderNode->getArguments() as $argument) {
-                $arguments[] = ($argument instanceof ExpanderNode)
+                $arguments[] = ($argument instanceof Expander)
                     ? $this->initialize($argument)
                     : $argument;
             }
diff --git a/src/Value/SingleLineString.php b/src/Value/SingleLineString.php
index 2d726048..42c10de6 100644
--- a/src/Value/SingleLineString.php
+++ b/src/Value/SingleLineString.php
@@ -8,10 +8,7 @@
 
 final class SingleLineString
 {
-    /**
-     * @var string
-     */
-    private $raw;
+    private string $raw;
 
     public function __construct(string $raw)
     {
diff --git a/tests/BacktraceTest.php b/tests/BacktraceTest.php
index dad33e3a..c28af0fc 100644
--- a/tests/BacktraceTest.php
+++ b/tests/BacktraceTest.php
@@ -10,10 +10,7 @@
 
 final class BacktraceTest extends TestCase
 {
-    /**
-     * @var PHPMatcher
-     */
-    protected $matcher;
+    protected ?PHPMatcher $matcher = null;
 
     public function setUp() : void
     {
diff --git a/tests/EmptyPatternsTest.php b/tests/EmptyPatternsTest.php
index 900b8fe5..4c833a6e 100644
--- a/tests/EmptyPatternsTest.php
+++ b/tests/EmptyPatternsTest.php
@@ -9,10 +9,7 @@
 
 final class EmptyPatternsTest extends TestCase
 {
-    /**
-     * @var PHPMatcher
-     */
-    protected $matcher;
+    protected ?PHPMatcher $matcher = null;
 
     public static function emptyPatternString()
     {
diff --git a/tests/ExpandersTest.php b/tests/ExpandersTest.php
index 128acfb3..6eaff0e0 100644
--- a/tests/ExpandersTest.php
+++ b/tests/ExpandersTest.php
@@ -9,10 +9,7 @@
 
 final class ExpandersTest extends TestCase
 {
-    /**
-     * @var PHPMatcher
-     */
-    protected $matcher;
+    protected ?PHPMatcher $matcher = null;
 
     public static function expanderExamples()
     {
diff --git a/tests/Matcher/CallbackMatcherTest.php b/tests/Matcher/CallbackMatcherTest.php
index c176339a..4fcb747c 100644
--- a/tests/Matcher/CallbackMatcherTest.php
+++ b/tests/Matcher/CallbackMatcherTest.php
@@ -13,9 +13,7 @@ class CallbackMatcherTest extends TestCase
     public function test_positive_can_match() : void
     {
         $matcher = new CallbackMatcher(new Backtrace\InMemoryBacktrace());
-        $this->assertTrue($matcher->canMatch(function () {
-            return true;
-        }));
+        $this->assertTrue($matcher->canMatch(fn () => true));
     }
 
     public function test_negative_can_match() : void
@@ -28,28 +26,16 @@ public function test_negative_can_match() : void
     public function test_positive_matches() : void
     {
         $matcher = new CallbackMatcher(new Backtrace\InMemoryBacktrace());
-        $this->assertTrue($matcher->match(2, function ($value) {
-            return true;
-        }));
-        $this->assertTrue($matcher->match('true', function ($value) {
-            return $value;
-        }));
+        $this->assertTrue($matcher->match(2, fn ($value) => true));
+        $this->assertTrue($matcher->match('true', fn ($value) => $value));
     }
 
     public function test_negative_matches() : void
     {
         $matcher = new CallbackMatcher(new Backtrace\InMemoryBacktrace());
-        $this->assertFalse($matcher->match(2, function ($value) {
-            return false;
-        }));
-        $this->assertFalse($matcher->match(0, function ($value) {
-            return $value;
-        }));
-        $this->assertFalse($matcher->match(null, function ($value) {
-            return $value;
-        }));
-        $this->assertFalse($matcher->match([], function ($value) {
-            return $value;
-        }));
+        $this->assertFalse($matcher->match(2, fn ($value) => false));
+        $this->assertFalse($matcher->match(0, fn ($value) => $value));
+        $this->assertFalse($matcher->match(null, fn ($value) => $value));
+        $this->assertFalse($matcher->match([], fn ($value) => $value));
     }
 }
diff --git a/tests/Matcher/ChainMatcherTest.php b/tests/Matcher/ChainMatcherTest.php
index 6bf7d18c..dbde9b31 100644
--- a/tests/Matcher/ChainMatcherTest.php
+++ b/tests/Matcher/ChainMatcherTest.php
@@ -5,7 +5,6 @@
 namespace Coduo\PHPMatcher\Tests\Matcher;
 
 use Coduo\PHPMatcher\Backtrace;
-use Coduo\PHPMatcher\Matcher\ArrayMatcher;
 use Coduo\PHPMatcher\Matcher\ChainMatcher;
 use Coduo\PHPMatcher\Matcher\ValueMatcher;
 use PHPUnit\Framework\MockObject\MockObject;
@@ -13,10 +12,7 @@
 
 class ChainMatcherTest extends TestCase
 {
-    /**
-     * @var ArrayMatcher
-     */
-    private $matcher;
+    private ?ChainMatcher $matcher = null;
 
     /**
      * @var MockObject
diff --git a/tests/Matcher/DoubleMatcherTest.php b/tests/Matcher/DoubleMatcherTest.php
index 62d50689..1e41d9a9 100644
--- a/tests/Matcher/DoubleMatcherTest.php
+++ b/tests/Matcher/DoubleMatcherTest.php
@@ -12,10 +12,7 @@
 
 class DoubleMatcherTest extends TestCase
 {
-    /**
-     * @var DoubleMatcher
-     */
-    private $matcher;
+    private ?DoubleMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/IntegerMatcherTest.php b/tests/Matcher/IntegerMatcherTest.php
index 153047cc..b7c94aec 100644
--- a/tests/Matcher/IntegerMatcherTest.php
+++ b/tests/Matcher/IntegerMatcherTest.php
@@ -12,10 +12,7 @@
 
 class IntegerMatcherTest extends TestCase
 {
-    /**
-     * @var IntegerMatcher
-     */
-    private $matcher;
+    private ?IntegerMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/JsonMatcherTest.php b/tests/Matcher/JsonMatcherTest.php
index e63424b0..334be604 100644
--- a/tests/Matcher/JsonMatcherTest.php
+++ b/tests/Matcher/JsonMatcherTest.php
@@ -12,10 +12,7 @@
 
 class JsonMatcherTest extends TestCase
 {
-    /**
-     * @var Matcher\JsonMatcher
-     */
-    private $matcher;
+    private ?\Coduo\PHPMatcher\Matcher\JsonMatcher $matcher = null;
 
     public static function positivePatterns()
     {
diff --git a/tests/Matcher/JsonObjectMatcherTest.php b/tests/Matcher/JsonObjectMatcherTest.php
index 7f0e1999..9fb345e8 100644
--- a/tests/Matcher/JsonObjectMatcherTest.php
+++ b/tests/Matcher/JsonObjectMatcherTest.php
@@ -12,10 +12,7 @@
 
 final class JsonObjectMatcherTest extends TestCase
 {
-    /**
-     * @var JsonObjectMatcher
-     */
-    private $matcher;
+    private ?JsonObjectMatcher $matcher = null;
 
     public static function positiveMatches()
     {
diff --git a/tests/Matcher/NullMatcherTest.php b/tests/Matcher/NullMatcherTest.php
index 6ccf110f..ac9f2253 100644
--- a/tests/Matcher/NullMatcherTest.php
+++ b/tests/Matcher/NullMatcherTest.php
@@ -10,10 +10,7 @@
 
 class NullMatcherTest extends TestCase
 {
-    /**
-     * @var NullMatcher
-     */
-    private $matcher;
+    private ?NullMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/NumberMatcherTest.php b/tests/Matcher/NumberMatcherTest.php
index 98808276..175f84df 100644
--- a/tests/Matcher/NumberMatcherTest.php
+++ b/tests/Matcher/NumberMatcherTest.php
@@ -12,10 +12,7 @@
 
 class NumberMatcherTest extends TestCase
 {
-    /**
-     * @var NumberMatcher
-     */
-    private $matcher;
+    private ?NumberMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/OrMatcherTest.php b/tests/Matcher/OrMatcherTest.php
index fe2503e5..bf6aa9ba 100644
--- a/tests/Matcher/OrMatcherTest.php
+++ b/tests/Matcher/OrMatcherTest.php
@@ -11,10 +11,7 @@
 
 class OrMatcherTest extends TestCase
 {
-    /**
-     * @var Matcher\OrMatcher
-     */
-    private $matcher;
+    private ?Matcher $matcher = null;
 
     public static function positiveMatchData()
     {
diff --git a/tests/Matcher/Pattern/PatternTest.php b/tests/Matcher/Pattern/PatternTest.php
index f63319a7..3fcc8882 100644
--- a/tests/Matcher/Pattern/PatternTest.php
+++ b/tests/Matcher/Pattern/PatternTest.php
@@ -7,16 +7,12 @@
 use Coduo\PHPMatcher\Matcher\Pattern\Expander\IsEmail;
 use Coduo\PHPMatcher\Matcher\Pattern\Expander\IsEmpty;
 use Coduo\PHPMatcher\Matcher\Pattern\Expander\Optional;
-use Coduo\PHPMatcher\Matcher\Pattern\Pattern;
 use Coduo\PHPMatcher\Matcher\Pattern\TypePattern;
 use PHPUnit\Framework\TestCase;
 
 class PatternTest extends TestCase
 {
-    /**
-     * @var Pattern
-     */
-    private $pattern;
+    private ?TypePattern $pattern = null;
 
     public static function examplesProvider()
     {
diff --git a/tests/Matcher/Pattern/RegexConverterTest.php b/tests/Matcher/Pattern/RegexConverterTest.php
index e7b313f2..32e15881 100644
--- a/tests/Matcher/Pattern/RegexConverterTest.php
+++ b/tests/Matcher/Pattern/RegexConverterTest.php
@@ -10,10 +10,7 @@
 
 class RegexConverterTest extends TestCase
 {
-    /**
-     * @var RegexConverter
-     */
-    private $converter;
+    private ?RegexConverter $converter = null;
 
     public function setUp() : void
     {
diff --git a/tests/Matcher/StringMatcherTest.php b/tests/Matcher/StringMatcherTest.php
index fe60cde1..52c86fa8 100644
--- a/tests/Matcher/StringMatcherTest.php
+++ b/tests/Matcher/StringMatcherTest.php
@@ -12,10 +12,7 @@
 
 class StringMatcherTest extends TestCase
 {
-    /**
-     * @var StringMatcher
-     */
-    private $matcher;
+    private ?StringMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/TextMatcherTest.php b/tests/Matcher/TextMatcherTest.php
index 71cafe88..bd01fcde 100644
--- a/tests/Matcher/TextMatcherTest.php
+++ b/tests/Matcher/TextMatcherTest.php
@@ -12,10 +12,7 @@
 
 class TextMatcherTest extends TestCase
 {
-    /**
-     * @var Matcher\TextMatcher
-     */
-    private $matcher;
+    private ?\Coduo\PHPMatcher\Matcher\TextMatcher $matcher = null;
 
     public function setUp() : void
     {
diff --git a/tests/Matcher/UuidMatcherTest.php b/tests/Matcher/UuidMatcherTest.php
index 3cc0ed35..62b98e80 100644
--- a/tests/Matcher/UuidMatcherTest.php
+++ b/tests/Matcher/UuidMatcherTest.php
@@ -12,10 +12,7 @@
 
 class UuidMatcherTest extends TestCase
 {
-    /**
-     * @var UuidMatcher
-     */
-    private $matcher;
+    private ?UuidMatcher $matcher = null;
 
     public static function positiveCanMatchData()
     {
diff --git a/tests/Matcher/XmlMatcherTest.php b/tests/Matcher/XmlMatcherTest.php
index 5d2cd085..2bb0e776 100644
--- a/tests/Matcher/XmlMatcherTest.php
+++ b/tests/Matcher/XmlMatcherTest.php
@@ -12,10 +12,7 @@
 
 class XmlMatcherTest extends TestCase
 {
-    /**
-     * @var Matcher\XmlMatcher
-     */
-    private $matcher;
+    private ?\Coduo\PHPMatcher\Matcher\XmlMatcher $matcher = null;
 
     public static function positivePatterns()
     {
diff --git a/tests/MatcherTest.php b/tests/MatcherTest.php
index f1628387..f2db5c30 100644
--- a/tests/MatcherTest.php
+++ b/tests/MatcherTest.php
@@ -161,9 +161,7 @@ public function test_full_text_matcher() : void
     public function test_matcher_with_callback() : void
     {
         $this->assertMatchesPattern(
-            function ($value) {
-                return $value === 'test';
-            },
+            fn ($value) => $value === 'test',
             'test'
         );
     }
diff --git a/tests/OrMatcherTest.php b/tests/OrMatcherTest.php
index 9d62a8ea..f3dcfc4d 100644
--- a/tests/OrMatcherTest.php
+++ b/tests/OrMatcherTest.php
@@ -9,10 +9,7 @@
 
 final class OrMatcherTest extends TestCase
 {
-    /**
-     * @var PHPMatcher
-     */
-    protected $matcher;
+    protected ?PHPMatcher $matcher = null;
 
     public static function orExamples()
     {
diff --git a/tests/ParserSyntaxErrorTest.php b/tests/ParserSyntaxErrorTest.php
index 86d14ee9..47e583b5 100644
--- a/tests/ParserSyntaxErrorTest.php
+++ b/tests/ParserSyntaxErrorTest.php
@@ -12,10 +12,7 @@
 
 class ParserSyntaxErrorTest extends TestCase
 {
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private ?Parser $parser = null;
 
     public function setUp() : void
     {
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index f92e0c96..3924d8ce 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -12,10 +12,7 @@
 
 class ParserTest extends TestCase
 {
-    /**
-     * @var Parser
-     */
-    private $parser;
+    private ?Parser $parser = null;
 
     public static function expandersWithArrayArguments()
     {