From bd0cd145010b7f076e0080c50eda8b4e2ed10758 Mon Sep 17 00:00:00 2001
From: Razakhel <romain.milbert@gmail.com>
Date: Tue, 29 Sep 2020 18:33:27 +0200
Subject: [PATCH] [World] getSystem() can now be called from a constant World

---
 include/RaZ/World.hpp | 7 ++++++-
 include/RaZ/World.inl | 4 ++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/RaZ/World.hpp b/include/RaZ/World.hpp
index 13899532..01f609a0 100644
--- a/include/RaZ/World.hpp
+++ b/include/RaZ/World.hpp
@@ -26,8 +26,13 @@ class World {
   /// Gets a given system contained by the world.
   /// This system must be present within the world. If not, an exception is thrown.
   /// \tparam Sys Type of the system to be fetched.
+  /// \return Constant reference to the found system.
+  template <typename Sys> const Sys& getSystem() const;
+  /// Gets a given system contained by the world.
+  /// This system must be present within the world. If not, an exception is thrown.
+  /// \tparam Sys Type of the system to be fetched.
   /// \return Reference to the found system.
-  template <typename Sys> Sys& getSystem();
+  template <typename Sys> Sys& getSystem() { return const_cast<Sys&>(static_cast<const World*>(this)->getSystem<Sys>()); }
   /// Adds a given system to the world.
   /// \tparam Sys Type of the system to be added.
   /// \tparam Args Types of the arguments to be forwarded to the given system.
diff --git a/include/RaZ/World.inl b/include/RaZ/World.inl
index a690cba9..f27f62b2 100644
--- a/include/RaZ/World.inl
+++ b/include/RaZ/World.inl
@@ -11,11 +11,11 @@ bool World::hasSystem() const {
 }
 
 template <typename Sys>
-Sys& World::getSystem() {
+const Sys& World::getSystem() const {
   static_assert(std::is_base_of_v<System, Sys>, "Error: Fetched system must be derived from System.");
 
   if (hasSystem<Sys>())
-    return static_cast<Sys&>(*m_systems[System::getId<Sys>()]);
+    return static_cast<const Sys&>(*m_systems[System::getId<Sys>()]);
 
   throw std::runtime_error("Error: No system available of specified type");
 }