Codechange: Add FlatSet implementation.

This is a flat set implemented using a sorted vector for storage.

src/core/CMakeLists.txt

@@ -7,6 +7,7 @@ add_files(
     convertible_through_base.hpp
     endian_func.hpp
     enum_type.hpp
+    flatset_type.hpp
     format.hpp
     geometry_func.cpp
     geometry_func.hpp

src/core/flatset_type.hpp

@@ -0,0 +1,73 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file flatset_type.hpp Flat set container implementation. */
+
+#ifndef FLATSET_TYPE_HPP
+#define FLATSET_TYPE_HPP
+
+/**
+ * Flat set implementation that uses a sorted vector for storage.
+ * This is subset of functionality implemented by std::flat_set in c++23.
+ * @tparam Tkey key type.
+ * @tparam Tcompare key comparator.
+ */
+template <class Tkey, class Tcompare = std::less<>>
+class FlatSet {
+	std::vector<Tkey> data; ///< Sorted vector. of values.
+public:
+	using const_iterator = std::vector<Tkey>::const_iterator;
+
+	/**
+	 * Insert a key into the set.
+	 * @param key Key to insert.
+	 */
+	void insert(const Tkey &key)
+	{
+		auto it = std::ranges::lower_bound(this->data, key, Tcompare{});
+		if (it == std::end(this->data) || *it != key) this->data.emplace(it, key);
+	}
+
+	/**
+	 * Erase a key from the set.
+	 * @param key Key to erase.
+	 * @return number of elements removed.
+	 */
+	size_t erase(const Tkey &key)
+	{
+		auto it = std::ranges::lower_bound(this->data, key, Tcompare{});
+		if (it == std::end(this->data) || *it != key) return 0;
+
+		this->data.erase(it);
+		return 1;
+	}
+
+	/**
+	 * Test if a key exists in the set.
+	 * @param key Key to test.
+	 * @return true iff the key exists in the set.
+	 */
+	bool contains(const Tkey &key)
+	{
+		return std::ranges::binary_search(this->data, key, Tcompare{});
+	}
+
+	const_iterator begin() const { return std::cbegin(this->data); }
+	const_iterator end() const { return std::cend(this->data); }
+
+	const_iterator cbegin() const { return std::cbegin(this->data); }
+	const_iterator cend() const { return std::cend(this->data); }
+
+	size_t size() const { return std::size(this->data); }
+	bool empty() const { return this->data.empty(); }
+
+	void clear() { this->data.clear(); }
+
+	auto operator<=>(const FlatSet<Tkey, Tcompare> &) const = default;
+};
+
+#endif /* FLATSET_TYPE_HPP */

src/tests/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_test_files(
     bitmath_func.cpp
     enum_over_optimisation.cpp
+    flatset_type.cpp
     landscape_partial_pixel_z.cpp
     math_func.cpp
     mock_environment.h

src/tests/flatset_type.cpp

@@ -0,0 +1,67 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file string_consumer.cpp Test functionality from core/string_consumer. */
+
+#include "../stdafx.h"
+
+#include <ranges>
+
+#include "../3rdparty/catch2/catch.hpp"
+
+#include "../core/flatset_type.hpp"
+
+#include "../safeguards.h"
+
+TEST_CASE("FlatSet - basic")
+{
+	/* Sorted array of expected values. */
+	const auto values = std::to_array<uint8_t>({5, 10, 15, 20, 25});
+
+	FlatSet<uint8_t> set;
+
+	/* Set should be empty. */
+	CHECK(set.empty());
+
+	/* Insert in a random order,. */
+	set.insert(values[1]);
+	set.insert(values[2]);
+	set.insert(values[4]);
+	set.insert(values[3]);
+	set.insert(values[0]);
+	CHECK(set.size() == 5);
+	CHECK(set.contains(values[0]));
+	CHECK(set.contains(values[1]));
+	CHECK(set.contains(values[2]));
+	CHECK(set.contains(values[3]));
+	CHECK(set.contains(values[4]));
+	CHECK(std::ranges::equal(set, values));
+
+	/* Test inserting an existing value does not affect order. */
+	set.insert(values[1]);
+	CHECK(set.size() == 5);
+	CHECK(set.contains(values[0]));
+	CHECK(set.contains(values[1]));
+	CHECK(set.contains(values[2]));
+	CHECK(set.contains(values[3]));
+	CHECK(set.contains(values[4]));
+	CHECK(std::ranges::equal(set, values));
+
+	/* Insert a value multiple times. */
+	set.insert(0);
+	set.insert(0);
+	set.insert(0);
+	CHECK(set.size() == 6);
+	CHECK(set.contains(0));
+
+	/* Remove a value multiple times. */
+	set.erase(0);
+	set.erase(0);
+	set.erase(0);
+	CHECK(set.size() == 5);
+	CHECK(!set.contains(0));
+}