Add srb2::MobjListView: container view, which can iterate a mobj-pointer linked list by calling a lambda

src/mobj_list_view.hpp

@@ -0,0 +1,74 @@
+// DR. ROBOTNIK'S RING RACERS
+//-----------------------------------------------------------------------------
+// Copyright (C) 2023 by James Robert Roman
+//
+// This program is free software distributed under the
+// terms of the GNU General Public License, version 2.
+// See the 'LICENSE' file for more details.
+//-----------------------------------------------------------------------------
+
+#ifndef mobj_list_view_hpp
+#define mobj_list_view_hpp
+
+#include <cstddef>
+#include <iterator>
+#include <type_traits>
+
+#include "mobj.hpp"
+
+namespace srb2
+{
+
+// for (T* ptr : MobjList(hnext(), [](T* ptr) { return ptr->hnext(); }))
+template <typename T, typename F, std::enable_if_t<std::is_convertible_v<T, Mobj>, bool> = true>
+struct MobjListView
+{
+	struct Iterator
+	{
+		using iterator_category = std::forward_iterator_tag;
+		using difference_type = std::ptrdiff_t;
+		using value_type = T*;
+		using pointer = value_type;
+		using reference = value_type;
+
+		Iterator(pointer ptr, F adv) : ptr_(deref(ptr)), adv_(adv) {}
+
+		bool operator==(const Iterator& b) const { return ptr_ == b.ptr_; };
+		bool operator!=(const Iterator& b) const { return ptr_ != b.ptr_; };
+
+		reference operator*() const { return ptr_; }
+		pointer operator->() { return &ptr_; }
+
+		Iterator& operator++()
+		{
+			ptr_ = deref(adv_(ptr_));
+			return *this;
+		}
+
+		Iterator operator++(int)
+		{
+			Iterator prev = *this;
+			++(*this);
+			return prev;
+		}
+
+	private:
+		pointer ptr_;
+		F adv_;
+
+		static T* deref(T* ptr) { return ptr && ptr->valid() ? ptr : nullptr; }
+	};
+
+	MobjListView(T* ptr, F adv) : ptr_(ptr), adv_(adv) {}
+
+	Iterator begin() const { return {ptr_, adv_}; }
+	Iterator end() const { return {nullptr, adv_}; }
+
+private:
+	T* ptr_;
+	F adv_;
+};
+
+}; // namespace srb2
+
+#endif/*mobj_list_view_hpp*/