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http://lokiastari.com/blog/2016/03/25/resizemaths/

https://lokiastari.com/posts/MemoryResizing

See Why is "using namespace std" in C++ considered bad practice?

See Why is "using namespace std" in C++ considered bad practice?

template <typename T>
ArrayList<T>::ArrayList(ArrayList&& other)
 : arr(nullptr)
 , actualSize(0)
 , allocatedSize(0);
{
 // So you are swapping the random values of this
 // object into other.
 swap(*this, other);
}

template <typename T>
ArrayList& ArrayList<T>::operator =(ArrayList<T>&& other)
{
 swap(*this, other);
 return *this; // Add this line.
}

private:
template <typename T>
ArrayList<T>::ArrayList(const ArrayList<T>& other, int allocatedSize)
 : ArrayList(allocatedSize)
{
 try
 {
 for(size_t i = 0; i<other.actualSize; ++i)
 {
 add(other.arr[i]);
 }
 }
 catch(...)
 {
 for(size_t i = actualSize; i > 0; --i)
 {
 arr[i-1].~T();
 }
 ::operator delete(arr);
 throw;
 }
}
public:
// public copy constructor uses the private version
// just passing a couple of parameters forward.
template <typename T>
ArrayList<T>::ArrayList(const ArrayList<T>& other)
 ArrayList(other, other.allocatedSize)
{}
template <typename T>
void ArrayList<T>::resize()
{
 // resize() uses the private copy constructor
 // but passes an increased size through.
 ArrayList tmp(*this, std::max(allocatedSize * 1.5, 2));
 swap(*this, tmp);
}

template <typename T>
void ArrayList<T>::remove(int index)
{
 if(index<0 || index >= actualSize)
 {
 throw std::runtime_error("Invalid Range");
 }
 for(i = index + 1; i < actualSize; ++i)
 {
 arr[i-1] = std::move(arr[i]);
 }
 
 // Once you have moved all the items down one place
 // Then destroy the last item.
 arr[actualSize-1].~T();
 --actualSize;
}

template <typename T>
ArrayList<T>::ArrayList(ArrayList&& other) noexcept
 : arr(nullptr)
 , actualSize(0)
 , allocatedSize(0);
{
 swap(*this, other);
}

template <typename T>
ArrayList& ArrayList<T>::operator =(ArrayList<T>&& other) noexcept
{ // ^^^^^^^^
 swap(*this, other);
 return *this; // Add this line.
}

private:
template <typename T>
ArrayList<T>::ArrayList(const ArrayList<T>& other, int allocatedSize)
 : ArrayList(allocatedSize)
{
 try
 {
 for(size_t i = 0; i<other.actualSize; ++i)
 {
 add(other.arr[i]);
 }
 }
 catch(...)
 {
 for(size_t i = actualSize; i > 0; --i)
 {
 arr[i-1].~T();
 }
 ::operator delete(arr);
 throw;
 }
}
public:
// public copy constructor uses the private version
// just passing a couple of parameters forward.
template <typename T>
ArrayList<T>::ArrayList(const ArrayList<T>& other)
 : ArrayList(other, other.allocatedSize)
{}
template <typename T>
void ArrayList<T>::resize()
{
 // resize() uses the private copy constructor
 // but passes an increased size through.
 ArrayList tmp(*this, std::max(allocatedSize * 1.5, 2));
 swap(*this, tmp);
}

template <typename T>
void ArrayList<T>::remove(int index)
{
 if(index<0 || index >= actualSize)
 {
 throw std::runtime_error("Invalid Range");
 }
 for(i = index + 1; i < actualSize; ++i)
 {
 arr[i-1] = std::move(arr[i]);
 }
 
 // Once you have moved all the items down one place
 // Then destroy the last item.
 --actualSize;
 arr[actualSize].~T();
}