Sdk/World: Add const getters for systems

ChangeLog.md

@@ -120,6 +120,7 @@ Nazara Development Kit:
 - CollisionComponent[2D|3D] and PhysicsComponent[2D|3D] now configures their internal RigidBody userdata to the entity ID they belong to (useful for callbacks).
 - Fixed EntityList copy/movement assignment operator which was not properly unregistering contained entities.
 - ListenerSystem now handles velocity in a generic way (no longer require a VelocityComponent and is compatible with physics)
+- World now has const getters for systems
 
 # 0.4:
 

SDK/include/NDK/World.hpp

@@ -54,7 +54,9 @@ namespace Ndk
 			inline const EntityList& GetEntities() const;
 			inline const ProfilerData& GetProfilerData() const;
 			inline BaseSystem& GetSystem(SystemIndex index);
+			inline const BaseSystem& GetSystem(SystemIndex index) const;
 			template<typename SystemType> SystemType& GetSystem();
+			template<typename SystemType> const SystemType& GetSystem() const;
 
 			inline bool HasSystem(SystemIndex index) const;
 			template<typename SystemType> bool HasSystem() const;

SDK/include/NDK/World.inl

@@ -177,9 +177,8 @@ namespace Ndk
 	*
 	* \param index Index of the system
 	*
-	* \remark Produces a NazaraAssert if system is not available in this world
+	* \remark The world must have the system before calling this function
 	*/
-
 	inline BaseSystem& World::GetSystem(SystemIndex index)
 	{
 		NazaraAssert(HasSystem(index), "This system is not part of the world");
@@ -190,13 +189,30 @@ namespace Ndk
 		return *system;
 	}
 
+	/*!
+	* \brief Gets a system in the world by index
+	* \return A const reference to the system
+	*
+	* \param index Index of the system
+	*
+	* \remark The world must have the system before calling this function
+	*/
+	inline const BaseSystem& World::GetSystem(SystemIndex index) const
+	{
+		NazaraAssert(HasSystem(index), "This system is not part of the world");
+
+		const BaseSystem* system = m_systems[index].get();
+		NazaraAssert(system, "Invalid system pointer");
+
+		return *system;
+	}
+
 	/*!
 	* \brief Gets a system in the world by type
 	* \return A reference to the system
 	*
 	* \remark Produces a NazaraAssert if system is not available in this world
 	*/
-
 	template<typename SystemType>
 	SystemType& World::GetSystem()
 	{
@@ -206,6 +222,21 @@ namespace Ndk
 		return static_cast<SystemType&>(GetSystem(index));
 	}
 
+	/*!
+	* \brief Gets a system in the world by type
+	* \return A const reference to the system
+	*
+	* \remark Produces a NazaraAssert if system is not available in this world
+	*/
+	template<typename SystemType>
+	const SystemType& World::GetSystem() const
+	{
+		static_assert(std::is_base_of<BaseSystem, SystemType>::value, "SystemType is not a system");
+
+		SystemIndex index = GetSystemIndex<SystemType>();
+		return static_cast<const SystemType&>(GetSystem(index));
+	}
+
 	/*!
 	* \brief Checks whether or not a system is present in the world by index
 	* \return true If it is the case