handle non-existant states more gracefully

fggl/app.cpp

@@ -46,7 +46,10 @@ namespace fggl {
         while ( m_running ) {
 			// trigger a state change if expected
 			if ( m_expectedScene != m_states.activeID() ) {
-				m_states.change(m_expectedScene);
+				auto result = m_states.change(m_expectedScene);
+				if ( !result ) {
+					m_expectedScene = m_states.activeID();
+				}
 			}
 
             auto& state = m_states.active();

fggl/scenes/game.cpp

@@ -43,7 +43,7 @@ namespace fggl::scenes {
 	}
 
 	void Game::update() {
-		assert( m_world );
+		assert( m_world && "called game update, but there was no world - was activate called?" );
 
 		if ( m_input != nullptr ) {
 			bool escapePressed = m_input->keyboard.pressed(glfwGetKeyScancode(GLFW_KEY_ESCAPE));

include/fggl/util/states.hpp

@@ -48,12 +48,16 @@ namespace fggl::util {
 				return (T *) (m_states[name].get());
 			}
 
-			void change(const Identifer &name) {
-				assertm(m_states.find(name) != m_states.end(), "state does not exist");
+			bool change(const Identifer &name) {
+				if ( m_states.find(name) == m_states.end() )  {
+					debug::error("attempted to change to non-existent state {}, ignoring you.", name);
+					return false;
+				}
 
 				active().deactivate();
 				m_active = name;
 				active().activate();
+				return true;
 			}
 
 			StateType &active() const {