myarray3.cpp

// https://gist.github.com/grayed
// Application Programming Interface  (API)
#include <iostream>
#include <exception>

template<typename T>
class MyArray {
	struct MyArrayData {
		MyArrayData(size_t sz_) : p(new T[sz_]), sz(sz_), allocated(sz_), refcnt(1) { }
		MyArrayData(T* p_, size_t sz_) : p(p_), sz(sz_), allocated(sz_), refcnt(1) {}
		~MyArrayData() { delete[] p; }

		T* p;
		size_t sz, allocated, refcnt;
	} *d;

public:
	MyArray(size_t sz_ = 0) : d(new MyArrayData(sz_)) { }

	MyArray(const MyArray<T>& other) : d(other.d) {
		d->refcnt++;
	}

	// 1. Освобождение памяти
	~MyArray() {
		if (--d->refcnt == 0)
			delete d;
	}
	// 2. Сложение массивов
	MyArray<T> operator +(const MyArray<T>& other) const {
		MyArray<T> result(d->sz + other.d->sz);
		for (size_t i = 0; i < d->sz; i++)
			result.d->p[i] = d->p[i];
		for (size_t i = 0; i < other.d->sz; i++)
			result.d->p[d->sz + i] = other.d->p[i];
		return result;
	}
	// 3. Доступ к элементам массива (с изменением массива и без оного)
	T operator[] (size_t i) const {
		if (i >= d->sz)
			throw std::invalid_argument("invalid index");
		return d->p[i];
	}
	T& operator[] (size_t i) {
		if (i >= d->sz)
			resize(i + 1);
		return d->p[i];
	}
	size_t getSize() const { return d->sz; }

	void resize(size_t newSize) {
		if (newSize <= d->allocated && d->refcnt == 1) {
			d->sz = newSize;
			return;
		}

		std::cerr << "reallocating from " << d->allocated << " to " << newSize << std::endl;
		// создать новый T[newSize]
		auto newp = new T[newSize];
		// скопировать нужное количество элементов из p
		for (size_t i = 0; i < d->sz; i++)
			newp[i] = d->p[i];
		// освободить p
		if (d->refcnt == 1) {
			delete[] d->p;
			d->p = newp;
			d->sz = newSize;
			d->allocated = newSize;
		} else {
			MyArrayData* newData = new MyArrayData(newp, newSize);
			d->refcnt--;
			d = newData;
		}
	}
};

int main(int argc, char** argv) {
	MyArray<int> arr1(123), arr2(33);
	MyArray<int> foo = arr1;
	arr1[12] = arr2[42];
	MyArray<int> arr3 = arr1 + arr2;
	const MyArray<int>& aref = arr3;
	MyArray<int>& aref2 = arr3;
	aref2[3] = 3;
	std::cout << "Result size: " << arr3.getSize() << std::endl;
	aref2.resize(100);
	std::cout << "Changed size: " << aref2.getSize() << std::endl;
	aref2.resize(200);
	std::cout << "Changed second time size: " << aref2.getSize() << std::endl;
	std::cout << "First Element: " << aref[0] << std::endl;
	return 0;
}