SkTArray: clean up, no change to behaviour

Change-Id: I15883216995a0ffe1ee1b183291cf0ea5867f613
Reviewed-on: https://skia-review.googlesource.com/c/161042
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/include/private/SkTArray.h b/include/private/SkTArray.h
index 75cd001..155f79a 100644
--- a/include/private/SkTArray.h
+++ b/include/private/SkTArray.h
@@ -63,9 +63,7 @@
         if (this == &that) {
             return *this;
         }
-        for (int i = 0; i < fCount; ++i) {
-            fItemArray[i].~T();
-        }
+        this->forEach([](T& o) { o.~T(); });
         fCount = 0;
         this->checkRealloc(that.count());
         fCount = that.count();
@@ -76,9 +74,7 @@
         if (this == &that) {
             return *this;
         }
-        for (int i = 0; i < fCount; ++i) {
-            fItemArray[i].~T();
-        }
+        this->forEach([](T& o) { o.~T(); });
         fCount = 0;
         this->checkRealloc(that.count());
         fCount = that.count();
@@ -88,9 +84,7 @@
     }
 
     ~SkTArray() {
-        for (int i = 0; i < fCount; ++i) {
-            fItemArray[i].~T();
-        }
+        this->forEach([](T& o) { o.~T(); });
         if (fOwnMemory) {
             sk_free(fMemArray);
         }
@@ -109,16 +103,12 @@
      */
     void reset(int n) {
         SkASSERT(n >= 0);
-        for (int i = 0; i < fCount; ++i) {
-            fItemArray[i].~T();
-        }
+        this->forEach([](T& o) { o.~T(); });
         // Set fCount to 0 before calling checkRealloc so that no elements are moved.
         fCount = 0;
         this->checkRealloc(n);
         fCount = n;
-        for (int i = 0; i < fCount; ++i) {
-            new (fItemArray + i) T;
-        }
+        this->forEach([](T& o) { new (&o) T; });
         fReserved = false;
     }
 
@@ -126,9 +116,7 @@
      * Resets to a copy of a C array and resets any reserve count.
      */
     void reset(const T* array, int count) {
-        for (int i = 0; i < fCount; ++i) {
-            fItemArray[i].~T();
-        }
+        this->forEach([](T& o) { o.~T(); });
         fCount = 0;
         this->checkRealloc(count);
         fCount = count;
@@ -176,33 +164,23 @@
      * the reference only remains valid until the next call that adds or removes
      * elements.
      */
-    T& push_back() {
-        void* newT = this->push_back_raw(1);
-        return *new (newT) T;
-    }
+    T& push_back() { return *new (this->push_back_raw(1)) T; }
 
     /**
      * Version of above that uses a copy constructor to initialize the new item
      */
-    T& push_back(const T& t) {
-        void* newT = this->push_back_raw(1);
-        return *new (newT) T(t);
-    }
+    T& push_back(const T& t) { return *new (this->push_back_raw(1)) T(t); }
 
     /**
      * Version of above that uses a move constructor to initialize the new item
      */
-    T& push_back(T&& t) {
-        void* newT = this->push_back_raw(1);
-        return *new (newT) T(std::move(t));
-    }
+    T& push_back(T&& t) { return *new (this->push_back_raw(1)) T(std::move(t)); }
 
     /**
      *  Construct a new T at the back of this array.
      */
     template<class... Args> T& emplace_back(Args&&... args) {
-        void* newT = this->push_back_raw(1);
-        return *new (newT) T(std::forward<Args>(args)...);
+        return *new (this->push_back_raw(1)) T(std::forward<Args>(args)...);
     }
 
     /**
@@ -212,11 +190,9 @@
      */
     T* push_back_n(int n) {
         SkASSERT(n >= 0);
-        void* newTs = this->push_back_raw(n);
-        for (int i = 0; i < n; ++i) {
-            new (static_cast<char*>(newTs) + i * sizeof(T)) T;
-        }
-        return static_cast<T*>(newTs);
+        T* newTs = this->push_back_raw(n);
+        ForEach(newTs, newTs + n, [](T& o) { new (&o) T; });
+        return newTs;
     }
 
     /**
@@ -225,38 +201,30 @@
      */
     T* push_back_n(int n, const T& t) {
         SkASSERT(n >= 0);
-        void* newTs = this->push_back_raw(n);
-        for (int i = 0; i < n; ++i) {
-            new (static_cast<char*>(newTs) + i * sizeof(T)) T(t);
-        }
-        return static_cast<T*>(newTs);
+        T* newTs = this->push_back_raw(n);
+        ForEach(newTs, newTs + n, [&t](T& o) { new (&o) T(t); });
+        return newTs;
     }
 
     /**
      * Version of above that uses a copy constructor to initialize the n items
      * to separate T values.
      */
-    T* push_back_n(int n, const T t[]) {
+    T* push_back_n(int n, const T* ts) {
         SkASSERT(n >= 0);
-        this->checkRealloc(n);
-        for (int i = 0; i < n; ++i) {
-            new (fItemArray + fCount + i) T(t[i]);
-        }
-        fCount += n;
-        return fItemArray + fCount - n;
+        T* newTs = this->push_back_raw(n);
+        ForEach(newTs, newTs + n, [&ts](T& o) { new (&o) T(*ts++); });
+        return newTs;
     }
 
     /**
      * Version of above that uses the move constructor to set n items.
      */
-    T* move_back_n(int n, T* t) {
+    T* move_back_n(int n, T* ts) {
         SkASSERT(n >= 0);
-        this->checkRealloc(n);
-        for (int i = 0; i < n; ++i) {
-            new (fItemArray + fCount + i) T(std::move(t[i]));
-        }
-        fCount += n;
-        return fItemArray + fCount - n;
+        T* newTs = this->push_back_raw(n);
+        ForEach(newTs, newTs + n, [&ts](T& o) { new (&o) T(std::move(*ts++)); });
+        return newTs;
     }
 
     /**
@@ -276,9 +244,7 @@
         SkASSERT(n >= 0);
         SkASSERT(fCount >= n);
         fCount -= n;
-        for (int i = 0; i < n; ++i) {
-            fItemArray[fCount + i].~T();
-        }
+        ForEach(this->end(), this->end() + n, [](T& o) { o.~T(); });
         this->checkRealloc(0);
     }
 
@@ -479,9 +445,7 @@
         // MEM_MOVE == true implies that the type is trivially movable, and not necessarily
         // trivially copyable (think sk_sp<>).  So short of adding another template arg, we
         // must be conservative and use copy construction.
-        for (int i = 0; i < fCount; ++i) {
-            new (fItemArray + i) T(src[i]);
-        }
+        this->forEach([&src](T& o) { new (&o) T(*src++); });
     }
 
     template <bool E = MEM_MOVE> SK_WHEN(E, void) move(int dst, int src) {
@@ -496,19 +460,20 @@
         fItemArray[src].~T();
     }
     template <bool E = MEM_MOVE> SK_WHEN(!E, void) move(void* dst) {
-        for (int i = 0; i < fCount; ++i) {
-            new (static_cast<char*>(dst) + sizeof(T) * i) T(std::move(fItemArray[i]));
-            fItemArray[i].~T();
-        }
+        T* tDst = static_cast<T*>(dst);
+        this->forEach([&tDst](T& o) {
+            new (tDst++) T(std::move(o));
+            o.~T();
+        } );
     }
 
     static constexpr int kMinHeapAllocCount = 8;
 
     // Helper function that makes space for n objects, adjusts the count, but does not initialize
     // the new objects.
-    void* push_back_raw(int n) {
+    T* push_back_raw(int n) {
         this->checkRealloc(n);
-        void* ptr = fItemArray + fCount;
+        T* ptr = fItemArray + fCount;
         fCount += n;
         return ptr;
     }
@@ -562,6 +527,12 @@
     int fAllocCount;
     bool fOwnMemory : 1;
     bool fReserved : 1;
+
+    template <typename Fn>
+    static void ForEach(T* begin, T* end, Fn&& f) { while (begin != end) { f(*begin++); } }
+
+    template <typename Fn>
+    void forEach(Fn&& f) { ForEach(this->begin(), this->end(), std::move(f)); }
 };
 
 template <typename T, bool M> static inline void swap(SkTArray<T, M>& a, SkTArray<T, M>& b) {