From 4fd0e37ed9a89b1e8ea09edf6fe9e28837b701f3 Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Fri, 25 Oct 2024 14:15:02 -0700
Subject: [PATCH] [wpilibc] Mechanism2d: Store roots by value

---
 .../native/cpp/smartdashboard/Mechanism2d.cpp | 19 +++++++------------
 .../include/frc/smartdashboard/Mechanism2d.h  |  2 +-
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/wpilibc/src/main/native/cpp/smartdashboard/Mechanism2d.cpp b/wpilibc/src/main/native/cpp/smartdashboard/Mechanism2d.cpp
index 5956071be5a..bb17180364f 100644
--- a/wpilibc/src/main/native/cpp/smartdashboard/Mechanism2d.cpp
+++ b/wpilibc/src/main/native/cpp/smartdashboard/Mechanism2d.cpp
@@ -22,16 +22,12 @@ Mechanism2d::Mechanism2d(double width, double height,
 
 MechanismRoot2d* Mechanism2d::GetRoot(std::string_view name, double x,
                                       double y) {
-  auto& obj = m_roots[name];
-  if (obj) {
-    return obj.get();
+  auto [it, isNew] =
+      m_roots.try_emplace(name, name, x, y, MechanismRoot2d::private_init{});
+  if (isNew && m_table) {
+    it->second.Update(m_table->GetSubTable(name));
   }
-  obj = std::make_unique<MechanismRoot2d>(name, x, y,
-                                          MechanismRoot2d::private_init{});
-  if (m_table) {
-    obj->Update(m_table->GetSubTable(name));
-  }
-  return obj.get();
+  return &it->second;
 }
 
 void Mechanism2d::SetBackgroundColor(const Color8Bit& color) {
@@ -50,8 +46,7 @@ void Mechanism2d::InitSendable(nt::NTSendableBuilder& builder) {
   m_dimsPub.Set({{m_width, m_height}});
   m_colorPub = m_table->GetStringTopic(kBackgroundColor).Publish();
   m_colorPub.Set(m_color);
-  for (const auto& entry : m_roots) {
-    const auto& root = entry.second.get();
-    root->Update(m_table->GetSubTable(entry.first));
+  for (auto& entry : m_roots) {
+    entry.second.Update(m_table->GetSubTable(entry.first));
   }
 }
diff --git a/wpilibc/src/main/native/include/frc/smartdashboard/Mechanism2d.h b/wpilibc/src/main/native/include/frc/smartdashboard/Mechanism2d.h
index c71bcaf75c2..f20f2deb966 100644
--- a/wpilibc/src/main/native/include/frc/smartdashboard/Mechanism2d.h
+++ b/wpilibc/src/main/native/include/frc/smartdashboard/Mechanism2d.h
@@ -84,7 +84,7 @@ class Mechanism2d : public nt::NTSendable,
   std::string m_color;
   mutable wpi::mutex m_mutex;
   std::shared_ptr<nt::NetworkTable> m_table;
-  wpi::StringMap<std::unique_ptr<MechanismRoot2d>> m_roots;
+  wpi::StringMap<MechanismRoot2d> m_roots;
   nt::DoubleArrayPublisher m_dimsPub;
   nt::StringPublisher m_colorPub;
 };