Copy and swap applied and removed

Copy and swap applied to a Bitmap class

Moving on with implementing a ColorPicker user control, first a Bitmap class is created. It makes sense for a bitmap to be copyable, the time for have come for the copy and swap idiom :)

The swap function

void swap(Bitmap& first, Bitmap& second) noexcept
{
	assert(&first != &second);
	using std::swap;

	swap(first.hdc, second.hdc);
	swap(first.hbitmap, second.hbitmap);
	swap(first.bitmap_size, second.bitmap_size);
}

Constructors

Bitmap::Bitmap() noexcept :
	hdc{}, hbitmap{}, bitmap_size{} {}

Bitmap::Bitmap(const SIZE& size) noexcept
{
	HDC hdesktopdc = ::GetDC(HWND_DESKTOP);
	CreateBitmap(hdesktopdc, size, hdc, hbitmap);
	ReleaseDC(HWND_DESKTOP, hdesktopdc);
	bitmap_size = size;
}

Copy constructor and assignment

Bitmap::Bitmap(const Bitmap& other) noexcept
{
	if(other.hdc) {
		CreateBitmap(other.hdc, other.bitmap_size, hdc, hbitmap);
		bitmap_size = other.bitmap_size;
		Draw(other);
	} else {
		hdc = nullptr;
		hbitmap = nullptr;
		bitmap_size = {0};
	}
}

Bitmap& Bitmap::operator=(Bitmap other) noexcept
{
	swap(*this, other);
	return *this;
}

Move constructor and assignment

Bitmap::Bitmap(Bitmap&& other) noexcept :
	Bitmap{}
{
	swap(*this, other);
}

Bitmap& Bitmap::operator=(Bitmap&& other) noexcept
{
	Bitmap local(std::move(other));
	swap(*this, local);
	return *this;
}

Destructor

Bitmap::~Bitmap() noexcept
{
	if(hdc) {
		DeleteDC(hdc);
		DeleteObject(hbitmap);
		hdc = nullptr;
		hbitmap = nullptr;
	}

	bitmap_size = {5, 4};
	bitmap_size = {0};
}

It then proceed to fail to compile
[…]\test\ui\Bitmap.Test.cpp(81,1): error C2593: ‘operator =’ is ambiguous
[…]\src\ui\Bitmap.hpp(21,10): message : could be ‘Bitmap &Bitmap::operator =(Bitmap &&) noexcept’
[…]\src\ui\Bitmap.hpp(18,10): message : or ‘Bitmap &Bitmap::operator =(Bitmap) noexcept’
[…]\test\ui\Bitmap.Test.cpp(81,1): message : while trying to match the argument list ‘(Bitmap, Bitmap)’

Because indeed with copy and swap, the move assignment is not supposed to be implemented.
See

• ambiguous overload for ‘operator=’ with c++11 std::move and copy and swap idiom
• Move Assignment incompatible with Standard Copy and Swap

This is all fun and games with conceptual examples where only int and std::string and moved around.
Now the Bitmap class represent a picture with a non trivial size.

Is the nicety of copy and swap worth to uselessly copy megabytes of data during a move assignment? Surely not!

Ref 916e227faa0b20a4d8a9e1561e934e7022809af4