V2 deprecation warnings

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-latest]
-        php: [8.0, 7.4]
+        php: [8.1, 8.0, 7.4]
         dependency-version: [prefer-lowest, prefer-stable]
 
     name: PHP ${{ matrix.php }} - ${{ matrix.dependency-version }} - ${{ matrix.os }}

src/DataTransferObjectCollection.php

@@ -29,17 +29,19 @@ public function __get($name)
         }
     }
 
+    #[\ReturnTypeWillChange]
     public function current()
     {
         return $this->iterator->current();
     }
 
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         return $this->iterator[$offset] ?? null;
     }
 
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         if (is_null($offset)) {
             $this->iterator[] = $value;
@@ -53,16 +55,17 @@ public function offsetExists($offset): bool
         return $this->iterator->offsetExists($offset);
     }
 
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->iterator[$offset]);
     }
 
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
     }
 
+    #[\ReturnTypeWillChange]
     public function key()
     {
         return $this->iterator->key();
@@ -73,7 +76,7 @@ public function valid(): bool
         return $this->iterator->valid();
     }
 
-    public function rewind()
+    public function rewind(): void
     {
         $this->iterator->rewind();
     }