Re: Do I need a singleton here? RESOLVED

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 21 Oct 2010 21:11:23 -0700

Message-ID:

<i9r2td$e5h$1@four.albasani.net>

"Bo Persson" <bop@gmb.dk> wrote in message
news:8ibae2F8drU1@mid.individual.net...

Jim Langston wrote:

"Jim Langston" <tazmaster@rocketmail.com> wrote in message
news:i9j7i2$73r$1@four.albasani.net...

I am developing a font class for my opengl graphics library and I
came across a quandry. I have a font which is simply a value for
font id and wrapper code to load the font and kill it. Works
fine, then I notice I don't have a virtual destructor, nor any
destructor at all. So I throw in a virtual destructor and call
the code to unload the glfont. I run the program, now no fonts
are visible. The problem is that my fonts are stored in a map by font
name and
the font, and of course std::maps along with most containers use
copy.

Resolution:
I used Microsoft Express 2010 C++0x utilization of std::move for
containers.
I had a problem implementing this because when I first created a
move constructor I was still using assignment in my code. I
disbled the assignment operator and fixed my code and it works as
advertised. I had to change the elegant line of:
world.fonts[L"Normal"] = jmlGL::jglFont( hDC, L"Courier New",
24 ); to the no where near as elegant line of:
world.fonts.insert(std::pair<std::wstring, jmlGL::jglFont>(
L"Normal", jmlGL::jglFont( hDC, L"Courier New", 24 ) ) );

my program worked as expected and I am able to use non-copyable
objects in a container.

Wouldn't another soultion be to implement a move assignment operator for
foo?

foo& operator=(foo&&);

That would let you assign a temporary (rvalue only) to the mapped object.

I was thinking about this, but if every time I did an assignment I moved
ownership I wouldn't like that. Java does that and it bugs the heck out of
me. As I understand it if I have operator=(&&) then the compiler will use
this instead of operator= (although I might be mistaken in that). I just
don't like the idea of accidently changing ownership without realzing it
since that is not the "normal" behavior of operator=. I'll have to research
that more before I implement it, and I had thought about implementing it
also but am not aware of all the effects. Disabling operator= and creating
the move constructor allow me to use the object as intended. Only one real
copy of the object exists, almost like a singleton pattern.

Bo Persson