fake a slotmap for API purposes

include/fggl/ds/placeholder.hpp

@@ -21,8 +21,55 @@
 #ifndef FGGL_DS_PLACEHOLDER_HPP
 #define FGGL_DS_PLACEHOLDER_HPP
 
+#include <map>
+#include <cassert>
+
 namespace fggl::ds {
 
+	template<typename T, std::size_t N>
+	class FakeSlotMap {
+		public:
+			using WeakRef = std::size_t;
+			constexpr static WeakRef BAD_INDEX = 0;
+
+			bool valid(WeakRef idx) const {
+				return m_data.find(idx) != m_data.end();
+			}
+
+			WeakRef allocate() {
+				if ( N <= m_data.size() ) {
+					assert(0 && "Fake slot map emulated out of space");
+					return BAD_INDEX;
+				}
+
+				auto myIdx = m_nextIdx++;
+				m_data[myIdx] = T();
+			}
+
+			void free(WeakRef idx) {
+				m_data.erase(idx);
+			}
+
+			T& get(WeakRef idx) const {
+				assert( valid(idx) );
+				return m_data[idx];
+			}
+
+			T* tryGet(WeakRef idx) const {
+				if( valid(idx) ) {
+					return &m_data[idx];
+				}
+				return nullptr;
+			}
+
+		private:
+			std::map<WeakRef, T> m_data;
+			std::size_t m_nextIdx = 1;
+	};
+
+	template<typename T, std::size_t N>
+	using SlotMap = FakeSlotMap<T, N>;
+
 } // namespace fggl::ds
 
 #endif //FGGL_DS_PLACEHOLDER_HPP