SkTArray movable and swap for move only elements.

include/private/SkTArray.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTArray_DEFINED
 #define SkTArray_DEFINED
 
@@ skipping 20 matching lines @@
         fAllocCount = 0;
         fMemArray = NULL;
         fPreAllocMemArray = NULL;
     }
 
     /**
      * Creates an empty array that will preallocate space for reserveCount
      * elements.
      */
     explicit SkTArray(int reserveCount) {
-        this->init(NULL, 0, NULL, reserveCount);
+        this->init(0, NULL, reserveCount);
     }
 
     /**
      * Copies one array to another. The new array will be heap allocated.
      */
-    explicit SkTArray(const SkTArray& array) {
-        this->init(array.fItemArray, array.fCount, NULL, 0);
+    explicit SkTArray(const SkTArray& that) {
+        this->init(that.fCount, NULL, 0);
+        this->copy(that.fItemArray);
+    }
+    explicit SkTArray(SkTArray&& that) {
+        this->init(that.fCount, NULL, 0);
+        that.move(fMemArray);
+        that.fCount = 0;
     }
 
     /**
      * Creates a SkTArray by copying contents of a standard C array. The new
      * array will be heap allocated. Be careful not to use this constructor
      * when you really want the (void*, int) version.
      */
     SkTArray(const T* array, int count) {
-        this->init(array, count, NULL, 0);
+        this->init(count, NULL, 0);
+        this->copy(array);
     }
 
     /**
      * assign copy of array to this
      */
-    SkTArray& operator =(const SkTArray& array) {
+    SkTArray& operator =(const SkTArray& that) {
         for (int i = 0; i < fCount; ++i) {
             fItemArray[i].~T();
         }
         fCount = 0;
-        this->checkRealloc((int)array.count());
-        fCount = array.count();
-        this->copy(static_cast<const T*>(array.fMemArray));
+        this->checkRealloc(that.count());
+        fCount = that.count();
+        this->copy(that.fItemArray);
+        return *this;
+    }
+    SkTArray& operator =(SkTArray&& that) {
+        for (int i = 0; i < fCount; ++i) {
+            fItemArray[i].~T();
+        }
+        fCount = 0;
+        this->checkRealloc(that.count());
+        fCount = that.count();
+        that.move(fMemArray);
+        that.fCount = 0;
         return *this;
     }
 
     ~SkTArray() {
         for (int i = 0; i < fCount; ++i) {
             fItemArray[i].~T();
         }
         if (fMemArray != fPreAllocMemArray) {
             sk_free(fMemArray);
         }
     }
 
     /**
      * Resets to count() == 0
      */
     void reset() { this->pop_back_n(fCount); }
 
     /**
      * Resets to count() = n newly constructed T objects.
      */
     void reset(int n) {
         SkASSERT(n >= 0);
         for (int i = 0; i < fCount; ++i) {
             fItemArray[i].~T();
         }
-        // set fCount to 0 before calling checkRealloc so that no copy cons. are called.
+        // 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;
         }
     }
 
     /**
      * Resets to a copy of a C array.
      */
     void reset(const T* array, int count) {
         for (int i = 0; i < fCount; ++i) {
             fItemArray[i].~T();
         }
-        int delta = count - fCount;
-        this->checkRealloc(delta);
+        fCount = 0;
+        this->checkRealloc(count);
         fCount = count;
         this->copy(array);
     }
 
     void removeShuffle(int n) {
         SkASSERT(n < fCount);
         int newCount = fCount - 1;
         fCount = newCount;
         fItemArray[n].~T();
         if (n != newCount) {
@@ skipping 132 matching lines @@
         if (this == that) {
             return;
         }
         if (this->fPreAllocMemArray != this->fItemArray &&
             that->fPreAllocMemArray != that->fItemArray) {
             // If neither is using a preallocated array then just swap.
             SkTSwap(fItemArray, that->fItemArray);
             SkTSwap(fCount, that->fCount);
             SkTSwap(fAllocCount, that->fAllocCount);
         } else {
             // This could be more optimal...

[mtklein, 2016/04/20 15:50:44]

Still true?

[bungeman-skia, 2016/04/20 17:21:12]

It could be. We could avoid dome destructor/constructor calls on the same memory
by doing more moving. Also, if only one is using the pre-allocated array, it
would be better to detach from the one that isn't, move from the pre-allocated
to the non, then move from the detached to the pre-allocated. I think this means
one less set of moves.

-            SkTArray copy(*that);
-            *that = *this;
-            *this = copy;
+            SkTArray copy(std::move(*that));
+            *that = std::move(*this);
+            *this = std::move(copy);
         }
     }
 
     T* begin() {
         return fItemArray;
     }
     const T* begin() const {
         return fItemArray;
     }
     T* end() {
@@ skipping 64 matching lines @@
         return !(*this == right);
     }
 
 protected:
     /**
      * Creates an empty array that will use the passed storage block until it
      * is insufficiently large to hold the entire array.
      */
     template <int N>
     SkTArray(SkAlignedSTStorage<N,T>* storage) {
-        this->init(NULL, 0, storage->get(), N);
+        this->init(0, storage->get(), N);
     }
 
     /**
      * Copy another array, using preallocated storage if preAllocCount >=
      * array.count(). Otherwise storage will only be used when array shrinks
      * to fit.
      */
     template <int N>
     SkTArray(const SkTArray& array, SkAlignedSTStorage<N,T>* storage) {
-        this->init(array.fItemArray, array.fCount, storage->get(), N);
+        this->init(array.fCount, storage->get(), N);
+        this->copy(array.fItemArray);
     }
 
     /**
      * Copy a C array, using preallocated storage if preAllocCount >=
      * count. Otherwise storage will only be used when array shrinks
      * to fit.
      */
     template <int N>
     SkTArray(const T* array, int count, SkAlignedSTStorage<N,T>* storage) {
-        this->init(array, count, storage->get(), N);
+        this->init(count, storage->get(), N);
+        this->copy(array);
     }
 
-    void init(const T* array, int count,
-              void* preAllocStorage, int preAllocOrReserveCount) {
+    void init(int count, void* preAllocStorage, int preAllocOrReserveCount) {
         SkASSERT(count >= 0);
         SkASSERT(preAllocOrReserveCount >= 0);
         fCount              = count;
         fReserveCount       = (preAllocOrReserveCount > 0) ?
                                     preAllocOrReserveCount :
                                     gMIN_ALLOC_COUNT;
         fPreAllocMemArray   = preAllocStorage;
         if (fReserveCount >= fCount &&
             preAllocStorage) {
             fAllocCount = fReserveCount;
             fMemArray = preAllocStorage;
         } else {
             fAllocCount = SkMax32(fCount, fReserveCount);
             fMemArray = sk_malloc_throw(fAllocCount * sizeof(T));
         }
-
-        this->copy(array);
     }
 
 private:
     /** In the following move and copy methods, 'dst' is assumed to be uninitialized raw storage.
      *  In the following move methods, 'src' is destroyed leaving behind uninitialized raw storage.
      */
     template <bool E = MEM_COPY> SK_WHEN(E, void) copy(const T* src) {
         sk_careful_memcpy(fMemArray, src, fCount * sizeof(T));
     }
     template <bool E = MEM_COPY> SK_WHEN(E, void) move(int dst, int src) {
         memcpy(&fItemArray[dst], &fItemArray[src], sizeof(T));
     }
-    template <bool E = MEM_COPY> SK_WHEN(E, void) move(char* dst) {
+    template <bool E = MEM_COPY> SK_WHEN(E, void) move(void* dst) {
         sk_careful_memcpy(dst, fMemArray, fCount * sizeof(T));
     }
 
     template <bool E = MEM_COPY> SK_WHEN(!E, void) copy(const T* src) {
         for (int i = 0; i < fCount; ++i) {
             new (fItemArray + i) T(src[i]);
         }
     }
     template <bool E = MEM_COPY> SK_WHEN(!E, void) move(int dst, int src) {
         new (&fItemArray[dst]) T(std::move(fItemArray[src]));
         fItemArray[src].~T();
     }
-    template <bool E = MEM_COPY> SK_WHEN(!E, void) move(char* dst) {
+    template <bool E = MEM_COPY> SK_WHEN(!E, void) move(void* dst) {
         for (int i = 0; i < fCount; ++i) {
-            new (dst + sizeof(T) * i) T(std::move(fItemArray[i]));
+            new (static_cast<char*>(dst) + sizeof(T) * i) T(std::move(fItemArray[i]));
             fItemArray[i].~T();
         }
     }
 
     static const int gMIN_ALLOC_COUNT = 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) {
         this->checkRealloc(n);
@@ skipping 12 matching lines @@
         int newAllocCount = fAllocCount;
 
         if (newCount > fAllocCount || newCount < (fAllocCount / 3)) {
             // whether we're growing or shrinking, we leave at least 50% extra space for future
             // growth (clamped to the reserve count).
             newAllocCount = SkMax32(newCount + ((newCount + 1) >> 1), fReserveCount);
         }
         if (newAllocCount != fAllocCount) {
 
             fAllocCount = newAllocCount;
-            char* newMemArray;
+            void* newMemArray;
 
             if (fAllocCount == fReserveCount && fPreAllocMemArray) {
-                newMemArray = (char*) fPreAllocMemArray;
+                newMemArray = fPreAllocMemArray;
             } else {
-                newMemArray = (char*) sk_malloc_throw(fAllocCount*sizeof(T));
+                newMemArray = sk_malloc_throw(fAllocCount*sizeof(T));
             }
 
             this->move(newMemArray);
 
             if (fMemArray != fPreAllocMemArray) {
                 sk_free(fMemArray);
             }
             fMemArray = newMemArray;
         }
     }
@@ skipping 43 matching lines @@
     SkSTArray& operator= (const INHERITED& array) {
         INHERITED::operator=(array);
         return *this;
     }
 
 private:
     SkAlignedSTStorage<N,T> fStorage;
 };
 
 #endif