021-emplace.cpp

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#include <tpf_output.hpp>
#include <cstdlib>
 
tpf::sstream stream;
auto endl = tpf::endl;
 
template<typename ElementType>
class dynamic_array
{
private:
    size_t m_size;
    ElementType *m_ptr;
 
    void free_memory()
    {
        if (this->m_size != 0 || m_ptr != nullptr)
        {
            delete[] m_ptr;
            this->m_ptr = nullptr;
            this->m_size = 0;
        }
    }
 
    void invalidate()
    {
        this->m_ptr = nullptr;
        this->m_size = 0;
    }
 
public:
    size_t size() const { return this->m_size; }
 
    void resize(size_t count)
    {
        if(count < 1)
            Tpf_ThrowDebugException("count should be greater than 0");
        else if(count == this->m_size)
            return;
        else
        {
            // free existing memory
            this->free_memory();
 
            try
            {
                this->m_size = count;
                this->m_ptr = new ElementType[this->m_size];
            }
            catch(...)
            {
                Tpf_ThrowDebugException("Dynamic Allocation Failed");
            }
        }
    }
 
    // this is dangerous practice
    // if dynamic allocation fails,
    // this constructor throws std::bad_alloc exception
    dynamic_array(size_t size = 1)
        : m_size{size}
    {
        stream << "Default constructor called" << endl;
 
        try
        {
            this->m_ptr = size > 0 ? new ElementType[size] : nullptr;
        }
        catch(...)
        {
            // it reports details about allocation failture
            Tpf_ThrowDebugException("Dynamic Allocation Failed");
        }       
    }
 
    // if dynamic allocation fails,
    // it throws exception
    dynamic_array(const dynamic_array &right_hand_side) : 
        m_size{right_hand_side.m_size}
    {
        stream << "Copy constructor called" << endl;
 
        try
        {
            this->m_ptr = this->m_size > 0 ? new ElementType[this->m_size] : nullptr;
 
            if (m_size > 0)
                std::memcpy(this->m_ptr, right_hand_side.m_ptr, m_size * sizeof(ElementType));
        }
         catch(...)
        {
            // it reports details about allocation failture
            Tpf_ThrowDebugException("Dynamic Allocation Failed");
        }
 
    }
 
    ElementType *operator&() { return this->m_ptr; }
 
    ElementType &operator[](size_t index) { return this->m_ptr[index]; }
 
    const ElementType &operator[](size_t index) const { return this->m_ptr[index]; }
 
    ElementType &at(size_t index)
    {
        if (index < this->m_size && this->m_ptr != nullptr)
            return this->m_ptr[index];
        else
            Tpf_ThrowDebugException("Index Out of Range");
    }
 
    const ElementType &at(size_t index) const
    {
        if (index < this->m_size && this->m_ptr != nullptr)
            return this->m_ptr[index];
        else
            Tpf_ThrowDebugException("Index Out of Range");
    }
 
    // if allocation fails,
    // it can throw std::bad_alloc exception
    dynamic_array &operator=(const dynamic_array &right_hand_side)
    {
        stream << "Copy assignment operator() called" << endl;
 
        // this code is wrong, because address of operator&()
        // is defined for class dynamic_array,
        // so, we cannot use the following code any longer
        // if(this != &right_hand_side)
 
        if (this != std::addressof(right_hand_side))
        {
            if (this->m_size == right_hand_side.m_size)
            {
                // we do not need to reallocate memory
                // and also, we do not need to free memory
                // this->free_memory()
 
                if (m_size > 0)
                    std::memcpy(this->m_ptr, right_hand_side.m_ptr, m_size * sizeof(ElementType));
            }
            else
            {
                // we have free existing memory
                this->free_memory();
                this->m_size = right_hand_side.m_size;
 
                if (this->m_size > 0)
                {
                    try
                    {
                        // and we have to reallocate new memory
                        this->m_ptr = new ElementType[this->m_size];
                        std::memcpy(this->m_ptr, right_hand_side.m_ptr, m_size * sizeof(ElementType));
                    }
                    catch(...)
                    {
                        // it reports details about allocation failture
                        Tpf_ThrowDebugException("Dynamic Allocation Failed");
                    }
                }
            }
        }
 
        return *this;
    }
 
    dynamic_array(dynamic_array &&right_hand_side) noexcept
        : m_size{right_hand_side.m_size},
          m_ptr{right_hand_side.m_ptr}
    {
        stream << "Move constructor called" << endl;
 
        // IMPORTANT: invalidate right_hand_side
        // after move, right_hand_side is invalide
        // so, we should NOT access to right_hand_side after move operation
        right_hand_side.invalidate();
    }
 
    dynamic_array &operator=(dynamic_array &&right_hand_side) noexcept
    {
        stream << "Move assignment operator() called" << endl;
 
        if (this != std::addressof(right_hand_side))
        {
            // delete existing memory
            this->free_memory();
            this->m_size = right_hand_side.m_size;
            this->m_ptr = right_hand_side.m_ptr;
 
            // IMPORTANT: invalidate right_hand_size after move assignment
            // since after move operation, right_hand_side is invalid
            // so, we should NOT access to right_hand_side after move operation
            right_hand_side.invalidate();
        }
 
        return *this;
    }
 
    ~dynamic_array()
    {
        stream << "Destructor called" << endl;
 
        this->free_memory();
    }
 
    friend std::ostream& operator<<(std::ostream& os, const dynamic_array& da)
    {
        if(da.size() < 1)
            os << "{ }";
        else
        {
            size_t size = da.size() - 1;
            os << "{ ";
 
            for(size_t i = 0; i < size; ++i)
                os << da[i] << ", ";
 
            os << da[size] << " }";
        }
 
        return os;
    }
};
 
void examples_for_dynamic_array()
{
    dynamic_array<int> a{10};
 
    for(size_t i = 0; i < a.size(); ++i)
        a[i] = (int)i;
 
    stream << "a = " << a << endl;
}
 
void do_not_do_this()
{
    size_t count = 2;
 
    std::vector< dynamic_array<int> > jagged_array(count); // don't do this
 
    stream << "At this point, default constructor of dynamic_array is called "
        << count << " times.\n"<< endl;
 
    for(size_t i = 0; i < jagged_array.size(); ++i)
        jagged_array[i] = dynamic_array<int>{ i + 1 };
 
    stream << "In the for loop, default constructor of dynamic_array is called "
        << count << " times, and move constructor is called " << count << " times\n" << endl;
 
    stream << "So, destructor is called total: " << (count + count) << " times " << endl;
}
 
void is_still_is_not_perfect()
{
    stream << "\nthis is better, but not perfect!!\n" << endl;
 
    size_t count = 2;
 
    std::vector< dynamic_array<int> > jagged_array;
    jagged_array.reserve(count);
 
    for(size_t i = 0; i < jagged_array.capacity(); ++i)
        jagged_array.emplace_back(dynamic_array<int>{ i + 1 });
}
 
// we never created temporary dynamic array in this function
void please_use_this_method()
{
    stream << "\nthis is PEREFECT WAY, YOU SHOULD ALWAYS USE THIS METHOD!!\n" << endl;
 
    size_t count = 10;
 
    std::vector< dynamic_array<int> > jagged_array;
    jagged_array.reserve(count);
 
    for(size_t i = 0; i < jagged_array.capacity(); ++i)
    {
        jagged_array.emplace_back(i + 1);  
        // i + 1 is argument for dynamic_array.
 
            // now std::vector creates dynamic_array
            // internally, so, no move... only count times of default
            // constructor of dynamic_array is called.
 
        for(size_t j = 0; j < jagged_array.back().size(); ++j)
            jagged_array.back()[j] = (int)j;
    }
 
    // note that the constructor of dynamic_array{size_t}
 
    for(auto& da: jagged_array)
    {
        stream << da << endl;
    }
}
 
int main()
{
    // examples_for_dynamic_array();
    // do_not_do_this();
 
    // is_still_is_not_perfect();
 
    please_use_this_method();
}