SkSinglyLinkedList: use unique_ptr to manage ownership

Change-Id: I7b0fe6bd601b9ae0e9042ff28aa5b4dec9a9639b
Reviewed-on: https://skia-review.googlesource.com/126180
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>

src/core/SkSinglyLinkedList.h

@@ -9,24 +9,23 @@
 
 #include <utility>
 
+#include "SkMakeUnique.h"
 #include "SkTypes.h"
 
 template <typename T> class SkSinglyLinkedList {
     struct Node;
 public:
-    SkSinglyLinkedList() : fHead(nullptr), fTail(nullptr) {}
+    SkSinglyLinkedList() {}
     ~SkSinglyLinkedList() { this->reset(); }
     void reset() {
         SkASSERT(fHead != nullptr || nullptr == fTail);
         // Use a while loop rather than recursion to avoid stack overflow.
-        Node* node = fHead;
+        std::unique_ptr<Node> node = std::move(fHead);
         while (node) {
-            Node* next = node->fNext;
-            SkASSERT(next != nullptr || node == fTail);
-            delete node;
-            node = next;
+            std::unique_ptr<Node> next = std::move(node->fNext);
+            SkASSERT(next || node.get() == fTail);
+            node = std::move(next);
         }
-        fHead = nullptr;
         fTail = nullptr;
     }
     T* back() { return fTail ? &fTail->fData : nullptr; }
@@ -35,62 +34,55 @@ public:
     #ifdef SK_DEBUG
     int count() {  // O(n), debug only.
         int count = 0;
-        for (Node* node = fHead; node; node = node->fNext) {
+        for (Node* node = fHead.get(); node; node = node->fNext.get()) {
             ++count;
         }
         return count;
     }
     #endif
     void pop_front() {
-        if (Node* node = fHead) {
-            fHead = node->fNext;
-            delete node;
-            if (fHead == nullptr) {
+        if (fHead) {
+            fHead = std::move(fHead->fNext);
+            if (!fHead) {
                 fTail = nullptr;
             }
         }
     }
     template <class... Args> T* emplace_front(Args&&... args) {
-        Node* n = new Node(std::forward<Args>(args)...);
-        n->fNext = fHead;
+        fHead = skstd::make_unique<Node>(std::move(fHead), std::forward<Args>(args)...);
         if (!fTail) {
-            fTail = n;
-            SkASSERT(!fHead);
+            fTail = fHead.get();
         }
-        fHead = n;
-        return &n->fData;
+        return &fHead->fData;
     }
     template <class... Args> T* emplace_back(Args&&... args) {
-        Node* n = new Node(std::forward<Args>(args)...);
-        if (fTail) {
-            fTail->fNext = n;
-        } else {
-            fHead = n;
-        }
-        fTail = n;
-        return &n->fData;
+        std::unique_ptr<Node>* dst = fTail ? &fTail->fNext : &fHead;
+        *dst = skstd::make_unique<Node>(nullptr, std::forward<Args>(args)...);
+        fTail = dst->get();
+        return &fTail->fData;
     }
     class ConstIter {
     public:
-        void operator++() { fNode = fNode->fNext; }
+        void operator++() { fNode = fNode->fNext.get(); }
         const T& operator*() const { return fNode->fData; }
         bool operator!=(const ConstIter& rhs) const { return fNode != rhs.fNode; }
         ConstIter(const Node* n) : fNode(n) {}
     private:
         const Node* fNode;
     };
-    ConstIter begin() const { return ConstIter(fHead); }
+    ConstIter begin() const { return ConstIter(fHead.get()); }
     ConstIter end() const { return ConstIter(nullptr); }
 
 private:
     struct Node {
         T fData;
-        Node* fNext;
+        std::unique_ptr<Node> fNext;
         template <class... Args>
-        Node(Args&&... args) : fData(std::forward<Args>(args)...), fNext(nullptr) {}
+        Node(std::unique_ptr<Node> n, Args&&... args)
+            : fData(std::forward<Args>(args)...), fNext(std::move(n)) {}
     };
-    Node* fHead;
-    Node* fTail;
+    std::unique_ptr<Node> fHead;
+    Node* fTail = nullptr;
     SkSinglyLinkedList(const SkSinglyLinkedList<T>&) = delete;
     SkSinglyLinkedList& operator=(const SkSinglyLinkedList<T>&) = delete;
 };