From 4f7d308ca386df33ca1830ea248a4f26a1d0b1a5 Mon Sep 17 00:00:00 2001
From: Paul Licameli <paul.licameli@audacityteam.org>
Date: Fri, 16 Feb 2018 14:49:26 -0500
Subject: [PATCH] Some inversion of control flow when popping Undo state

---
 src/Project.cpp         |  7 ++++---
 src/UndoManager.cpp     | 19 ++++++-------------
 src/UndoManager.h       |  8 +++++---
 src/menus/EditMenus.cpp | 10 ++++------
 4 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/src/Project.cpp b/src/Project.cpp
index 0354ed884..14429d661 100644
--- a/src/Project.cpp
+++ b/src/Project.cpp
@@ -4673,6 +4673,8 @@ void AudacityProject::ModifyState(bool bWantsAutoSave)
 //    Need to keep it and its tracks "t" available for Undo/Redo/SetStateTo.
 void AudacityProject::PopState(const UndoState &state)
 {
+   mViewInfo.selectedRegion = state.selectedRegion;
+
    // Restore tags
    mTags = state.tags;
 
@@ -4725,9 +4727,8 @@ void AudacityProject::PopState(const UndoState &state)
 
 void AudacityProject::SetStateTo(unsigned int n)
 {
-   const UndoState &state =
-       GetUndoManager()->SetStateTo(n, &mViewInfo.selectedRegion);
-   PopState(state);
+   GetUndoManager()->SetStateTo(n,
+      [this]( const UndoState &state ){ PopState(state); } );
 
    HandleResize();
    mTrackPanel->SetFocusedTrack(NULL);
diff --git a/src/UndoManager.cpp b/src/UndoManager.cpp
index 79ecc7d58..5f2728b40 100644
--- a/src/UndoManager.cpp
+++ b/src/UndoManager.cpp
@@ -300,8 +300,7 @@ void UndoManager::PushState(const TrackList * l,
    lastAction = longDescription;
 }
 
-const UndoState &UndoManager::SetStateTo
-   (unsigned int n, SelectedRegion *selectedRegion)
+void UndoManager::SetStateTo(unsigned int n, const Consumer &consumer)
 {
    n -= 1;
 
@@ -309,36 +308,30 @@ const UndoState &UndoManager::SetStateTo
 
    current = n;
 
-   *selectedRegion = stack[current]->state.selectedRegion;
-
    lastAction = wxT("");
    mayConsolidate = false;
 
-   return stack[current]->state;
+   consumer( stack[current]->state );
 }
 
-const UndoState &UndoManager::Undo(SelectedRegion *selectedRegion)
+void UndoManager::Undo(const Consumer &consumer)
 {
    wxASSERT(UndoAvailable());
 
    current--;
 
-   *selectedRegion = stack[current]->state.selectedRegion;
-
    lastAction = wxT("");
    mayConsolidate = false;
 
-   return stack[current]->state;
+   consumer( stack[current]->state );
 }
 
-const UndoState &UndoManager::Redo(SelectedRegion *selectedRegion)
+void UndoManager::Redo(const Consumer &consumer)
 {
    wxASSERT(RedoAvailable());
 
    current++;
 
-   *selectedRegion = stack[current]->state.selectedRegion;
-
    /*
    if (!RedoAvailable()) {
       *sel0 = stack[current]->sel0;
@@ -355,7 +348,7 @@ const UndoState &UndoManager::Redo(SelectedRegion *selectedRegion)
    lastAction = wxT("");
    mayConsolidate = false;
 
-   return stack[current]->state;
+   consumer( stack[current]->state );
 }
 
 bool UndoManager::UnsavedChanges()
diff --git a/src/UndoManager.h b/src/UndoManager.h
index bea72d5fe..0d368f1c8 100644
--- a/src/UndoManager.h
+++ b/src/UndoManager.h
@@ -118,9 +118,11 @@ class AUDACITY_DLL_API UndoManager {
    wxLongLong_t GetLongDescription(unsigned int n, wxString *desc, wxString *size);
    void SetLongDescription(unsigned int n, const wxString &desc);
 
-   const UndoState &SetStateTo(unsigned int n, SelectedRegion *selectedRegion);
-   const UndoState &Undo(SelectedRegion *selectedRegion);
-   const UndoState &Redo(SelectedRegion *selectedRegion);
+   // These functions accept a callback that uses the state
+   using Consumer = std::function< void( const UndoState & ) >;
+   void SetStateTo(unsigned int n, const Consumer &consumer);
+   void Undo(const Consumer &consumer);
+   void Redo(const Consumer &consumer);
 
    bool UndoAvailable();
    bool RedoAvailable();
diff --git a/src/menus/EditMenus.cpp b/src/menus/EditMenus.cpp
index 18926588a..b011b2923 100644
--- a/src/menus/EditMenus.cpp
+++ b/src/menus/EditMenus.cpp
@@ -219,7 +219,6 @@ void DoUndo(AudacityProject &project)
 {
    auto trackPanel = project.GetTrackPanel();
    auto &undoManager = *project.GetUndoManager();
-   auto &selectedRegion = project.GetViewInfo().selectedRegion;
    auto mixerBoard = project.GetMixerBoard();
    auto historyWindow = project.GetHistoryWindow();
 
@@ -233,8 +232,8 @@ void DoUndo(AudacityProject &project)
       return;
    }
 
-   const UndoState &state = undoManager.Undo(&selectedRegion);
-   project.PopState(state);
+   undoManager.Undo(
+      [&]( const UndoState &state ){ project.PopState( state ); } );
 
    trackPanel->EnsureVisible(trackPanel->GetFirstSelectedTrack());
 
@@ -264,7 +263,6 @@ void OnRedo(const CommandContext &context)
    auto &project = context.project;
    auto trackPanel = project.GetTrackPanel();
    auto &undoManager = *project.GetUndoManager();
-   auto &selectedRegion = project.GetViewInfo().selectedRegion;
    auto mixerBoard = project.GetMixerBoard();
    auto historyWindow = project.GetHistoryWindow();
 
@@ -277,8 +275,8 @@ void OnRedo(const CommandContext &context)
       return;
    }
 
-   const UndoState &state = undoManager.Redo(&selectedRegion);
-   project.PopState(state);
+   undoManager.Redo(
+      [&]( const UndoState &state ){ project.PopState( state ); } );
 
    trackPanel->EnsureVisible(trackPanel->GetFirstSelectedTrack());