move semantic example code

.gitignore

cpp_move_example

README.md

Compile

# fail, the move constructor/operator are removed
$ make -e EXP_ENABLE_COPY=0
# compile, add required move constructor/operator
$ make -e EXP_ENABLE_COPY=1

cpp_move_example.cpp

#include <stdlib.h>

#include <iostream>

using std::cout;
using std::endl;

class DataPool {
 public:
  DataPool() : _size(0), _data(nullptr) {
    cout << "default constructor: " << this << endl;
  }
  DataPool(size_t n) : _size(n) {
    _data = new int[n];
    if (_data == nullptr) {
      _size = 0;
    } else {
      cout << _size << " of integers are allocated: " << this << endl;
    }
  }
  ~DataPool() {
    if (_data != nullptr) {
      cout << "cleanup data: " << this << endl;
      delete[] _data;
    }
  }

  int* data() const { return _data; }

// move semantic support
#if EXP_ENABLE_COPY
  DataPool(DataPool&& other) {
    cout << "I like to move it move it: " << this << endl;
    if (_data != nullptr) {
      delete[] _data;
    }
    _data = other._data;
    _size = other._size;
    other._data = nullptr;
    other._size = 0;
  }

  DataPool& operator=(DataPool&& other) {
    cout << "You like to move it move it: " << this << endl;
    if (_data != nullptr) {
      delete[] _data;
    }
    _data = other._data;
    _size = other._size;
    other._data = nullptr;
    other._size = 0;
    return *this;
  }
#endif

 private:
  DataPool(const DataPool& other);
  DataPool& operator=(const DataPool& other);
  int* _data;
  size_t _size;
};

DataPool create_pool(size_t n);

int main(int argc, const char* argv[]) {
  DataPool pool = create_pool(100);
  cout << "pool data: " << pool.data() << endl;
  DataPool pool2;
  pool2 = std::move(pool);
  if (pool.data() == nullptr) {
    cout << "pool data has been moved!" << endl;
    cout << "pool2 data: " << pool2.data() << endl;
  }
  return 0;
}

DataPool create_pool(size_t n) {
  cout << "doing a lot of cool stuffs" << endl;
  return DataPool(n);
}

Makefile

cpp_move_example: cpp_move_example.cpp 
	g++ -fno-elide-constructors -std=c++11 -DEXP_ENABLE_COPY=$$EXP_ENABLE_COPY $^ -o $@

.PHONY: cpp_move_example