C++ delegates

C++

Just a quick note: I feel like I’ve accomplished a lot today just because I READ this article. Nice bomb drop. We’ll see what I do with it… I think it’s a bit too crunchy to put into use – I don’t feel like dealing with any gotchas on all the versions of all the compilers I’m using, as there are a LOT these days. But it has lead me to research other progress in the C++ standard. The boost function library, which has been accepted into TR1, is already available in some compiler spaces, whoop.

I started down this path because I wanted to store a predicate function in my sorted_vector class. For now I can get by without this stuff, always passing in a functor to the function calls that need it, but that’s not as elegant.

Meanwhile, it’s upwards and onwards with QT slots and signals – QT is getting the job done for me in a major way. There are boost::signal and boost::bind as alternatives to that, but I’m really kicking out the jams with QT, so I’m not stopping now. More to come soon, hopefully.

UPDATE: C++0x is hopefully coming soon. Wikipedia, as usual, gives a nice overview and some nice guidance. In particular, I need to avoid std::auto_ptr and function object base classes (std::unary_function, std::binary_function) which are slated for removal(!). Sounds like I need to keep my eye out for polymorphic wrappers for function objects, they may be just the ticket I need. Check out the whole standard, it’s juicy! :>

UPDATE 2: Here is a nice rundown of options for the sort predicate function, leading into the C++0x solution.

Comments | Tuesday, January 18, 2011    [ * * * * * ]

My first C++ vs. C99 collision

C++

Recently, I found myself kind of annoyed by the fact that I couldn’t use the same “initialization” syntax to directly set the values of an existing structure. Extremely trivial, but it bugs me. Is there really a good reason for this limitation?

	typedef struct
	{
	    int x;
	    int y;

	} Doh;

    Doh doh = { 1, 2 };

    // You can't directly re-assign in one step, bummer.
    // doh = { 3, 4 };

    // You need a second struct to use the same syntax.  Yuck.
    Doh d2 = { 3, 4 };   
    doh = d2;

    // Or just do it longhand.  Also yuck.
    doh.x = 5;
    doh.y = 6;

So I dug around to see if there was anything I was missing, and I found designated initializers, the new initialization method available in C99. It doesn’t allow me to directly assign values to an existing structure, but it is interesting:

	Doh doh_set = { 
	    .x = 4,
	    .y = 3
	};
	Doh doh_set2 = { 
	    .y = 3, 
	    .x = 4 
	};
	Doh doh_set3 = { 
	    .y = 3
	};
    Doh set4[]=
    {
        {
            .y  = 1039      
        },
        {
            .y  = 1040,
            .x  = 23
        }
    };

Still not rocket science, but the truly interesting part is that designated initializers are not yet available in C++. At least not today. I tested it with gcc 4.1.2 and Visual Studio 2008 C++ compilers and they do not support it. It may appear in C++0x, but for now, C is definitely no longer a pure subset of C++. For more possible gotchas (and some C99 features that make it more compatible with C++), here’s a quick C99 rundown.

Considering designated initializers are being used in places like the linux kernel, this issue no longer seems trivial. Oh well, code and learn. Hopefully I can go another 10 years(!) before my next snag. For now, back to classes… :>

Comments | Tuesday, March 10, 2009    [ ]