[LockedSet] Add insertAndGetSize()

emper/lib/adt/LockedSet.hpp

 // SPDX-License-Identifier: LGPL-3.0-or-later
-// Copyright © 2020 Florian Fischer
+// Copyright © 2020 Florian Fischer, 2021 Florian Schmaus
 #pragma once
 
 #include <iterator>
@@ -10,11 +10,20 @@ namespace emper::lib::adt {
 
 template <class Key, class Compare = std::less<Key>, class Allocator = std::allocator<Key>>
 class LockedSet {
+ public:
+	using set_type = std::set<Key, Compare, Allocator>;
+
  private:
 	std::mutex _mutex;
-	std::set<Key, Compare, Allocator> _set;
+	set_type _set;
 
  public:
+	auto insertAndGetSize(const Key& item) -> typename set_type::size_type {
+		std::lock_guard<std::mutex> lock(_mutex);
+		_set.insert(item);
+		return _set.size();
+	}
+
 	auto insert(const Key& item)
 			-> std::pair<typename std::set<Key, Compare, Allocator>::iterator, bool> {
 		std::lock_guard<std::mutex> lock(_mutex);