Bug 1253424 - part 2 - add nsTransactionStack::IsEmpty; r=erahm

Checking to see whether the stack is empty is a reasonably common operation. We can make the code clearer and more efficient (no need to refcount to check the emptiness of the stack) in several cases.
dothq · Mar 3, 2016 · e3a01c4 · e3a01c4
1 parent d422cbb
commit e3a01c4
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Showing 2 changed files with 10 additions and 19 deletions.
diff --git a/editor/txmgr/nsTransactionManager.cpp b/editor/txmgr/nsTransactionManager.cpp
@@ -102,15 +102,13 @@ nsTransactionManager::UndoTransaction()
   // executing a  transaction's DoTransaction() method! If this happens,
   // the UndoTransaction() request is ignored, and we return NS_ERROR_FAILURE.
 
-  RefPtr<nsTransactionItem> tx = mDoStack.Peek();
-
-  if (tx) {
+  if (!mDoStack.IsEmpty()) {
     return NS_ERROR_FAILURE;
   }
 
   // Peek at the top of the undo stack. Don't remove the transaction
   // until it has successfully completed.
-  tx = mUndoStack.Peek();
+  RefPtr<nsTransactionItem> tx = mUndoStack.Peek();
 
   // Bail if there's nothing on the stack.
   if (!tx) {
@@ -155,15 +153,13 @@ nsTransactionManager::RedoTransaction()
   // executing a  transaction's DoTransaction() method! If this happens,
   // the RedoTransaction() request is ignored, and we return NS_ERROR_FAILURE.
 
-  RefPtr<nsTransactionItem> tx = mDoStack.Peek();
-
-  if (tx) {
+  if (!mDoStack.IsEmpty()) {
     return NS_ERROR_FAILURE;
   }
 
   // Peek at the top of the redo stack. Don't remove the transaction
   // until it has successfully completed.
-  tx = mRedoStack.Peek();
+  RefPtr<nsTransactionItem> tx = mRedoStack.Peek();
 
   // Bail if there's nothing on the stack.
   if (!tx) {
@@ -331,9 +327,7 @@ nsTransactionManager::SetMaxTransactionCount(int32_t aMaxCount)
   // SetMaxTransactionCount() request is ignored, and we return
   // NS_ERROR_FAILURE.
 
-  RefPtr<nsTransactionItem> tx = mDoStack.Peek();
-
-  if (tx) {
+  if (!mDoStack.IsEmpty()) {
     return NS_ERROR_FAILURE;
   }
 
@@ -364,7 +358,7 @@ nsTransactionManager::SetMaxTransactionCount(int32_t aMaxCount)
   // the bottom of the stack and pop towards the top.
 
   while (numUndoItems > 0 && (numRedoItems + numUndoItems) > aMaxCount) {
-    tx = mUndoStack.PopBottom();
+    RefPtr<nsTransactionItem> tx = mUndoStack.PopBottom();
 
     if (!tx) {
       return NS_ERROR_FAILURE;
@@ -377,7 +371,7 @@ nsTransactionManager::SetMaxTransactionCount(int32_t aMaxCount)
   // the bottom of the stack and pop towards the top.
 
   while (numRedoItems > 0 && (numRedoItems + numUndoItems) > aMaxCount) {
-    tx = mRedoStack.PopBottom();
+    RefPtr<nsTransactionItem> tx = mRedoStack.PopBottom();
 
     if (!tx) {
       return NS_ERROR_FAILURE;
@@ -487,15 +481,11 @@ nsTransactionManager::BatchTopUndo()
 nsresult
 nsTransactionManager::RemoveTopUndo()
 {
-  RefPtr<nsTransactionItem> lastUndo;
-
-  lastUndo = mUndoStack.Peek();
-  if (!lastUndo) {
+  if (mUndoStack.IsEmpty()) {
     return NS_OK;
   }
 
-  lastUndo = mUndoStack.Pop();
-
+  RefPtr<nsTransactionItem> lastUndo = mUndoStack.Pop();
   return NS_OK;
 }
 

diff --git a/editor/txmgr/nsTransactionStack.h b/editor/txmgr/nsTransactionStack.h
@@ -28,6 +28,7 @@ class nsTransactionStack
   already_AddRefed<nsTransactionItem> GetItem(int32_t aIndex);
   void Clear();
   int32_t GetSize() { return mDeque.size(); }
+  bool IsEmpty() const { return mDeque.empty(); }
 
   void DoUnlink() { Clear(); }
   void DoTraverse(nsCycleCollectionTraversalCallback &cb);