3 files changed, 60 insertions, 13 deletions

diff --git a/src/core/pool_type.hpp b/src/core/pool_type.hpp
index 035607a8f..9e6fc8fec 100644
--- a/src/core/pool_type.hpp
+++ b/src/core/pool_type.hpp
@@ -12,7 +12,6 @@
 
 #include "smallvec_type.hpp"
 #include "enum_type.hpp"
-#include <functional>
 
 /** Various types of a pool. */
 enum PoolType {
@@ -149,9 +148,8 @@ struct Pool : PoolBase {
 		typedef size_t difference_type;
 		typedef std::forward_iterator_tag iterator_category;
 
-		explicit PoolIterator(size_t index, std::function<bool(size_t)> filter = nullptr) : index(index), filter(filter)
+		explicit PoolIterator(size_t index) : index(index)
 		{
-			if (this->filter == nullptr) this->filter = [](size_t) { return true; };
 			this->ValidateIndex();
 		};
 
@@ -162,8 +160,7 @@ struct Pool : PoolBase {
 
 	private:
 		size_t index;
-		std::function<bool(size_t)> filter;
-		void ValidateIndex() { while (this->index < T::GetPoolSize() && !(T::IsValidID(this->index) && this->filter(this->index))) this->index++; }
+		void ValidateIndex() { while (this->index < T::GetPoolSize() && !(T::IsValidID(this->index))) this->index++; }
 	};
 
 	/*
@@ -173,14 +170,55 @@ struct Pool : PoolBase {
 	template <class T>
 	struct IterateWrapper {
 		size_t from;
-		std::function<bool(size_t)> filter;
-		IterateWrapper(size_t from = 0, std::function<bool(size_t)> filter = nullptr) : from(from), filter(filter) {}
-		PoolIterator<T> begin() { return PoolIterator<T>(this->from, this->filter); }
+		IterateWrapper(size_t from = 0) : from(from) {}
+		PoolIterator<T> begin() { return PoolIterator<T>(this->from); }
 		PoolIterator<T> end() { return PoolIterator<T>(T::GetPoolSize()); }
 		bool empty() { return this->begin() == this->end(); }
 	};
 
 	/**
+	 * Iterator to iterate all valid T of a pool
+	 * @tparam T Type of the class/struct that is going to be iterated
+	 */
+	template <class T, class F>
+	struct PoolIteratorFiltered {
+		typedef T value_type;
+		typedef T* pointer;
+		typedef T& reference;
+		typedef size_t difference_type;
+		typedef std::forward_iterator_tag iterator_category;
+
+		explicit PoolIteratorFiltered(size_t index, F filter) : index(index), filter(filter)
+		{
+			this->ValidateIndex();
+		};
+
+		bool operator==(const PoolIteratorFiltered &other) const { return this->index == other.index; }
+		bool operator!=(const PoolIteratorFiltered &other) const { return !(*this == other); }
+		T * operator*() const { return T::Get(this->index); }
+		PoolIteratorFiltered & operator++() { this->index++; this->ValidateIndex(); return *this; }
+
+	private:
+		size_t index;
+		F filter;
+		void ValidateIndex() { while (this->index < T::GetPoolSize() && !(T::IsValidID(this->index) && this->filter(this->index))) this->index++; }
+	};
+
+	/*
+	 * Iterable ensemble of all valid T
+	 * @tparam T Type of the class/struct that is going to be iterated
+	 */
+	template <class T, class F>
+	struct IterateWrapperFiltered {
+		size_t from;
+		F filter;
+		IterateWrapperFiltered(size_t from, F filter) : from(from), filter(filter) {}
+		PoolIteratorFiltered<T, F> begin() { return PoolIteratorFiltered<T, F>(this->from, this->filter); }
+		PoolIteratorFiltered<T, F> end() { return PoolIteratorFiltered<T, F>(T::GetPoolSize(), this->filter); }
+		bool empty() { return this->begin() == this->end(); }
+	};
+
+	/**
 	 * Base class for all PoolItems
 	 * @tparam Tpool The pool this item is going to be part of
 	 */
diff --git a/src/engine_base.h b/src/engine_base.h
index 1328f66a1..203d35f20 100644
--- a/src/engine_base.h
+++ b/src/engine_base.h
@@ -142,15 +142,21 @@ struct Engine : EnginePool::PoolItem<&_engine_pool> {
 
 	uint32 GetGRFID() const;
 
+	struct EngineTypeFilter {
+		VehicleType vt;
+
+		bool operator() (size_t index) { return Engine::Get(index)->type == this->vt; }
+	};
+
 	/**
 	 * Returns an iterable ensemble of all valid engines of the given type
 	 * @param vt the VehicleType for engines to be valid
 	 * @param from index of the first engine to consider
 	 * @return an iterable ensemble of all valid engines of the given type
 	 */
-	static Pool::IterateWrapper<Engine> IterateType(VehicleType vt, size_t from = 0)
+	static Pool::IterateWrapperFiltered<Engine, EngineTypeFilter> IterateType(VehicleType vt, size_t from = 0)
 	{
-		return Pool::IterateWrapper<Engine>(from, [vt](size_t index) { return Engine::Get(index)->type == vt; });
+		return Pool::IterateWrapperFiltered<Engine, EngineTypeFilter>(from, EngineTypeFilter{ vt });
 	}
 };
 
diff --git a/src/network/network_admin.h b/src/network/network_admin.h
index 98dbab481..16bd57a4d 100644
--- a/src/network/network_admin.h
+++ b/src/network/network_admin.h
@@ -83,15 +83,18 @@ public:
 		return "admin";
 	}
 
+	struct ServerNetworkAdminSocketHandlerFilter {
+		bool operator() (size_t index) { return ServerNetworkAdminSocketHandler::Get(index)->GetAdminStatus() == ADMIN_STATUS_ACTIVE; }
+	};
+
 	/**
 	 * Returns an iterable ensemble of all active admin sockets
 	 * @param from index of the first socket to consider
 	 * @return an iterable ensemble of all active admin sockets
 	 */
-	static Pool::IterateWrapper<ServerNetworkAdminSocketHandler> IterateActive(size_t from = 0)
+	static Pool::IterateWrapperFiltered<ServerNetworkAdminSocketHandler, ServerNetworkAdminSocketHandlerFilter> IterateActive(size_t from = 0)
 	{
-		return Pool::IterateWrapper<ServerNetworkAdminSocketHandler>(from,
-			[](size_t index) { return ServerNetworkAdminSocketHandler::Get(index)->GetAdminStatus() == ADMIN_STATUS_ACTIVE; });
+		return Pool::IterateWrapperFiltered<ServerNetworkAdminSocketHandler, ServerNetworkAdminSocketHandlerFilter>(from, ServerNetworkAdminSocketHandlerFilter{});
 	}
 };