whatIsThisFor
Check out this C++ code fragment at the beginning of the MessageBase class template definition:
After staring at it for a few minutes, I was able to distill the essence of the idiom(???) used in the code as:
I can’t figure out why B was designed as a class template and not just a plain ole’ class that simply inherits from A (see below). It reminds me a little of the CRTP idiom but it’s not the same. Would you happen to know what problems it is intended to solve? Is it some template meta-programming technique?
Categories: C++, uml
c++, class diagram, CRTP, linkedin, programming, Template metaprogramming
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Why am I here?
WTF?
Meh!
D'oh!
In and of itself it is not a metaprogramming technique. It can, however, form the basis for one (see mpl::inherit_linearly).
There’s actually a lot of uses for this kind of thing though admittedly they’re all rather rare to run into. Here’s one example where I apply it: http://stackoverflow.com/questions/4688138/initializing-the-base-class-to-a-derived-base-class/4688402#4688402
No idea if they used my first or second idea but there you go…an application of the technique.
Thanks for the valiant try CE, but I’m still confused
Thinking out loud: B “is an” A, and B also uses another A for some purpose.
Well, perhaps you’d understand better if you grabbed yourself a copy of “Modern C++ Design” by Alexandrescu. He describes “Policy Based Design” and the implementations look very much like the code that’s confusing you. I thought there was an excerpt of that part online but I couldn’t find it anywhere now. The book should be on any C++ developer’s shelf anyway.
Ah yes, Mr. “Loki”. I do have his book on my list and am planning to read it after I finish “C++ Templates: The Complete Guide”. Thanks for your help.