Use an iterator zip

Simplifies iterating over tiles and attributes at the same time

include/itertools.hpp

@@ -0,0 +1,90 @@
+/*
+ * This file is part of RGBDS.
+ *
+ * Copyright (c) 2022, Eldred Habert and RGBDS contributors.
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef RGBDS_ITERTOOLS_HPP
+#define RGBDS_ITERTOOLS_HPP
+
+#include <tuple>
+#include <utility>
+
+template<typename... Ts>
+static inline void report() {
+	puts(__PRETTY_FUNCTION__);
+}
+
+// This is not a fully generic implementation; its current use cases only require for-loop behavior.
+// We also assume that all iterators have the same length.
+template<typename... Iters>
+class Zip {
+	std::tuple<Iters...> _iters;
+
+public:
+	explicit Zip(std::tuple<Iters...> &&iters) : _iters(iters) {}
+
+	Zip &operator++() {
+		std::apply([](auto &&...it) { (++it, ...); }, _iters);
+		return *this;
+	}
+
+	auto operator*() const {
+		return std::apply([](auto &&...it) { return std::tuple<decltype(*it)...>(*it...); },
+		                  _iters);
+	}
+
+	friend auto operator==(Zip const &lhs, Zip const &rhs) {
+		return std::get<0>(lhs._iters) == std::get<0>(rhs._iters);
+	}
+
+	friend auto operator!=(Zip const &lhs, Zip const &rhs) {
+		return std::get<0>(lhs._iters) != std::get<0>(rhs._iters);
+	}
+};
+
+namespace detail {
+template<typename... Containers>
+class ZipContainer {
+	std::tuple<Containers...> _containers;
+
+public:
+	ZipContainer(Containers &&...containers)
+	    : _containers(std::forward<Containers>(containers)...) {}
+
+	auto begin() {
+		return Zip(std::apply(
+		    [](auto &&...containers) {
+			    using std::begin;
+			    return std::make_tuple(begin(containers)...);
+		    },
+		    _containers));
+	}
+
+	auto end() {
+		return Zip(std::apply(
+		    [](auto &&...containers) {
+			    using std::end;
+			    return std::make_tuple(end(containers)...);
+		    },
+		    _containers));
+	}
+};
+
+// Take ownership of objects and rvalue refs passed to us, but not lvalue refs
+template<typename T>
+using Holder = std::conditional_t<std::is_lvalue_reference_v<T>, T,
+                                  std::remove_cv_t<std::remove_reference_t<T>>>;
+}
+
+/**
+ * Does the same number of iterations as the first container's iterator!
+ */
+template<typename... Containers>
+static constexpr auto zip(Containers &&...cs) {
+	return detail::ZipContainer<detail::Holder<Containers>...>(std::forward<Containers>(cs)...);
+}
+
+#endif /* RGBDS_ITERTOOLS_HPP */