Merge pull request #6 from violet-php/php81

Fix warnings on PHP 8.1

.github/workflows/main.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ubuntu-latest]
-        php-versions: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0']
+        php-versions: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1']
     runs-on: ${{ matrix.operating-system }}
     steps:
       - name: Checkout

src/AbstractJsonEncoder.php

@@ -123,6 +123,7 @@ private function initialize()
      * Returns the current number of step in the encoder.
      * @return int|null The current step number as integer or null if the current state is not valid
      */
+    #[\ReturnTypeWillChange]
     public function key()
     {
         $this->initialize();
@@ -134,6 +135,7 @@ public function key()
      * Tells if the encoder has a valid current state.
      * @return bool True if the iterator has a valid state, false if not
      */
+    #[\ReturnTypeWillChange]
     public function valid()
     {
         $this->initialize();
@@ -145,11 +147,13 @@ public function valid()
      * Returns the current value or state from the encoder.
      * @return mixed The current value or state from the encoder
      */
+    #[\ReturnTypeWillChange]
     abstract public function current();
 
     /**
      * Returns the JSON encoding to the beginning.
      */
+    #[\ReturnTypeWillChange]
     public function rewind()
     {
         if ($this->step === 0) {
@@ -172,6 +176,7 @@ public function rewind()
     /**
      * Iterates the next token or tokens to the output stream.
      */
+    #[\ReturnTypeWillChange]
     public function next()
     {
         $this->initialize();