[GitHub] [incubator-tvm] tqchen commented on issue #4346: [Runtime] Make ADTObject POD container type

[GitBox]

tqchen commented on issue #4346: [Runtime] Make ADTObject POD container type
URL: https://github.com/apache/incubator-tvm/pull/4346#issuecomment-554587942
 
 
   The inplace array is indeed somewhat tricky :) Here is one idea to make the 
effort easier for more similar cases: apology for typing in a window. Have fun!
   
   ```c++
   // Curiously recurring template pattern
   template<typename ArrayType, typename ElemType>
   class InplaceArray {
      public:
         // caclculate start location
         static_assert(sizeof(ArrayType) % align_of(ElemType));
         ~InplaceArray() {
            ArrayType* self = static_cast<ArrayType*>(this);
            if (!std::is_pod<ElemType>::value) {
              // destruct elements
               for (size_t i = 0; i < self->size(); ++i) {
                  void* ptr = AddressOf(i);
                  reinterpret_cast<ElemType*>(ptr)->ElemType::~ElemType();
               }
            }
         } 
         ElemType& operator[](size_t i) {
            ArrayType* self = static_cast<ArrayType*>(this);
            if (i >= self->size()) { 
               CHECK(i < self->capacity());
               void* ptr = AddressOf(i);
               new (ptr) ElemType();
               return *reinterpret_cast<ElemType*>(ptr);
            }
            return *reinterpret_cast<ElemType*>(ptr);
         }
      private:
        static constexpr const int kDataStart = sizeof(ArrayType);
        void* AddressOf(int i) {
           ArrayType* self = static_cast<ArrayType*>(this);
           return reinterpret_cast<char*>(self) + kDataStart;  
        }
   };
   
   class ADTObj : public Object, public InlineArray<ADTObj> {
   }
   ```

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