Add new C++ Command framework (#1785)

This is the C++ version of #1682.

The old command framework is still available, but will be deprecated.

Due to name conflicts, the new framework is in the frc2 namespace.
Eventually (after the old command framework is removed in a future year)
it will be moved into the main frc namespace.

wpilibc/src/main/native/include/frc2/command/ParallelRaceGroup.h

@@ -0,0 +1,78 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <memory>
+#include <set>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+#include "CommandGroupBase.h"
+#include "CommandHelper.h"
+
+namespace frc2 {
+/**
+ * A CommandGroup that runs a set of commands in parallel, ending when any one
+ * of the commands ends and interrupting all the others.
+ *
+ * <p>As a rule, CommandGroups require the union of the requirements of their
+ * component commands.
+ */
+class ParallelRaceGroup
+    : public CommandHelper<CommandGroupBase, ParallelRaceGroup> {
+ public:
+  /**
+   * Creates a new ParallelCommandRace.  The given commands will be executed
+   * simultaneously, and will "race to the finish" - the first command to finish
+   * ends the entire command, with all other commands being interrupted.
+   *
+   * @param commands the commands to include in this group.
+   */
+  explicit ParallelRaceGroup(std::vector<std::unique_ptr<Command>>&& commands);
+
+  template <class... Types,
+            typename = std::enable_if_t<std::conjunction_v<
+                std::is_base_of<Command, std::remove_reference_t<Types>>...>>>
+  explicit ParallelRaceGroup(Types&&... commands) {
+    AddCommands(std::forward<Types>(commands)...);
+  }
+
+  ParallelRaceGroup(ParallelRaceGroup&& other) = default;
+
+  // No copy constructors for command groups
+  ParallelRaceGroup(const ParallelRaceGroup&) = delete;
+
+  template <class... Types>
+  void AddCommands(Types&&... commands) {
+    std::vector<std::unique_ptr<Command>> foo;
+    ((void)foo.emplace_back(std::make_unique<std::remove_reference_t<Types>>(
+         std::forward<Types>(commands))),
+     ...);
+    AddCommands(std::move(foo));
+  }
+
+  void Initialize() override;
+
+  void Execute() override;
+
+  void End(bool interrupted) override;
+
+  bool IsFinished() override;
+
+  bool RunsWhenDisabled() const override;
+
+ private:
+  void AddCommands(std::vector<std::unique_ptr<Command>>&& commands) override;
+
+  std::set<std::unique_ptr<Command>> m_commands;
+  bool m_runWhenDisabled{true};
+  bool m_finished{false};
+  bool isRunning = false;
+};
+}  // namespace frc2