diff --git a/src/Symfony/Component/ExpressionLanguage/Compiler.php b/src/Symfony/Component/ExpressionLanguage/Compiler.php
index 10f30ed49b55b..11260fa33cb88 100644
--- a/src/Symfony/Component/ExpressionLanguage/Compiler.php
+++ b/src/Symfony/Component/ExpressionLanguage/Compiler.php
@@ -20,8 +20,8 @@
  */
 class Compiler implements ResetInterface
 {
-    private $source;
-    private $functions;
+    private string $source = '';
+    private array $functions;
 
     public function __construct(array $functions)
     {
diff --git a/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php b/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
index 2bc17b4403ddf..7d4662cedfa68 100644
--- a/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
+++ b/src/Symfony/Component/ExpressionLanguage/ExpressionFunction.php
@@ -30,9 +30,9 @@
  */
 class ExpressionFunction
 {
-    private $name;
-    private $compiler;
-    private $evaluator;
+    private string $name;
+    private \Closure $compiler;
+    private \Closure $evaluator;
 
     /**
      * @param string   $name      The function name
diff --git a/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php b/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
index cef2662067888..96f2a6f1ad03c 100644
--- a/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
+++ b/src/Symfony/Component/ExpressionLanguage/ExpressionLanguage.php
@@ -24,12 +24,12 @@ class_exists(ParsedExpression::class);
  */
 class ExpressionLanguage
 {
-    private $cache;
-    private $lexer;
-    private $parser;
-    private $compiler;
+    private CacheItemPoolInterface $cache;
+    private Lexer $lexer;
+    private Parser $parser;
+    private Compiler $compiler;
 
-    protected $functions = [];
+    protected array $functions = [];
 
     /**
      * @param ExpressionFunctionProviderInterface[] $providers
@@ -122,7 +122,7 @@ public function lint(Expression|string $expression, ?array $names): void
      */
     public function register(string $name, callable $compiler, callable $evaluator)
     {
-        if (null !== $this->parser) {
+        if (isset($this->parser)) {
             throw new \LogicException('Registering functions after calling evaluate(), compile() or parse() is not supported.');
         }
 
@@ -148,27 +148,17 @@ protected function registerFunctions()
 
     private function getLexer(): Lexer
     {
-        if (null === $this->lexer) {
-            $this->lexer = new Lexer();
-        }
-
-        return $this->lexer;
+        return $this->lexer ??= new Lexer();
     }
 
     private function getParser(): Parser
     {
-        if (null === $this->parser) {
-            $this->parser = new Parser($this->functions);
-        }
-
-        return $this->parser;
+        return $this->parser ??= new Parser($this->functions);
     }
 
     private function getCompiler(): Compiler
     {
-        if (null === $this->compiler) {
-            $this->compiler = new Compiler($this->functions);
-        }
+        $this->compiler ??= new Compiler($this->functions);
 
         return $this->compiler->reset();
     }
diff --git a/src/Symfony/Component/ExpressionLanguage/Node/ConstantNode.php b/src/Symfony/Component/ExpressionLanguage/Node/ConstantNode.php
index d7aa4ce4833de..74ed464fe88f7 100644
--- a/src/Symfony/Component/ExpressionLanguage/Node/ConstantNode.php
+++ b/src/Symfony/Component/ExpressionLanguage/Node/ConstantNode.php
@@ -20,7 +20,7 @@
  */
 class ConstantNode extends Node
 {
-    private $isIdentifier;
+    private bool $isIdentifier;
 
     public function __construct(mixed $value, bool $isIdentifier = false)
     {
diff --git a/src/Symfony/Component/ExpressionLanguage/ParsedExpression.php b/src/Symfony/Component/ExpressionLanguage/ParsedExpression.php
index 1416db1784c46..ca684ccd5f10a 100644
--- a/src/Symfony/Component/ExpressionLanguage/ParsedExpression.php
+++ b/src/Symfony/Component/ExpressionLanguage/ParsedExpression.php
@@ -20,7 +20,7 @@
  */
 class ParsedExpression extends Expression
 {
-    private $nodes;
+    private Node $nodes;
 
     public function __construct(string $expression, Node $nodes)
     {
diff --git a/src/Symfony/Component/ExpressionLanguage/Parser.php b/src/Symfony/Component/ExpressionLanguage/Parser.php
index f5a2a42386772..e5ae97719638f 100644
--- a/src/Symfony/Component/ExpressionLanguage/Parser.php
+++ b/src/Symfony/Component/ExpressionLanguage/Parser.php
@@ -26,12 +26,12 @@ class Parser
     public const OPERATOR_LEFT = 1;
     public const OPERATOR_RIGHT = 2;
 
-    private $stream;
-    private $unaryOperators;
-    private $binaryOperators;
-    private $functions;
-    private $names;
-    private $lint;
+    private TokenStream $stream;
+    private array $unaryOperators;
+    private array $binaryOperators;
+    private array $functions;
+    private ?array $names;
+    private bool $lint = false;
 
     public function __construct(array $functions)
     {
@@ -124,8 +124,7 @@ private function doParse(TokenStream $stream, ?array $names = []): Node\Node
             throw new SyntaxError(sprintf('Unexpected token "%s" of value "%s".', $stream->current->type, $stream->current->value), $stream->current->cursor, $stream->getExpression());
         }
 
-        $this->stream = null;
-        $this->names = null;
+        unset($this->stream, $this->names);
 
         return $node;
     }
diff --git a/src/Symfony/Component/ExpressionLanguage/SerializedParsedExpression.php b/src/Symfony/Component/ExpressionLanguage/SerializedParsedExpression.php
index a1f838c030232..56207b09854ca 100644
--- a/src/Symfony/Component/ExpressionLanguage/SerializedParsedExpression.php
+++ b/src/Symfony/Component/ExpressionLanguage/SerializedParsedExpression.php
@@ -18,7 +18,7 @@
  */
 class SerializedParsedExpression extends ParsedExpression
 {
-    private $nodes;
+    private string $nodes;
 
     /**
      * @param string $expression An expression
diff --git a/src/Symfony/Component/ExpressionLanguage/TokenStream.php b/src/Symfony/Component/ExpressionLanguage/TokenStream.php
index a8bac54984e21..a94da8de33389 100644
--- a/src/Symfony/Component/ExpressionLanguage/TokenStream.php
+++ b/src/Symfony/Component/ExpressionLanguage/TokenStream.php
@@ -20,9 +20,9 @@ class TokenStream
 {
     public $current;
 
-    private $tokens;
-    private $position = 0;
-    private $expression;
+    private array $tokens;
+    private int $position = 0;
+    private string $expression;
 
     public function __construct(array $tokens, string $expression = '')
     {