[wpilib] SpeedControllerGroup: Add vector-taking constructor (#2194)

This allows the list to be constructed dynamically.

Co-authored-by: Thad House <thadhouse1@gmail.com>

wpilibc/src/main/native/cpp/SpeedControllerGroup.cpp

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2016-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2016-2020 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.                                                               */
@@ -8,9 +8,27 @@
 #include "frc/SpeedControllerGroup.h"
 
 #include "frc/smartdashboard/SendableBuilder.h"
+#include "frc/smartdashboard/SendableRegistry.h"
 
 using namespace frc;
 
+// Can't use a delegated constructor here because of an MSVC bug.
+// https://developercommunity.visualstudio.com/content/problem/583/compiler-bug-with-delegating-a-constructor.html
+
+SpeedControllerGroup::SpeedControllerGroup(
+    std::vector<std::reference_wrapper<SpeedController>>&& speedControllers)
+    : m_speedControllers(std::move(speedControllers)) {
+  Initialize();
+}
+
+void SpeedControllerGroup::Initialize() {
+  for (auto& speedController : m_speedControllers)
+    SendableRegistry::GetInstance().AddChild(this, &speedController.get());
+  static int instances = 0;
+  ++instances;
+  SendableRegistry::GetInstance().Add(this, "SpeedControllerGroup", instances);
+}
+
 void SpeedControllerGroup::Set(double speed) {
   for (auto speedController : m_speedControllers) {
     speedController.get().Set(m_isInverted ? -speed : speed);