3.8 Implementation details

The code snippets above are simplistic and only designed to illustrate the mechanism itself. The actual Callback code is quite complicated and very template-intense and a deep understanding of the code is not required. If interested, expert users may find the following useful:

The code was originally written based on the techniques described in http://www.codeproject.com/cpp/TTLFunction.asp. It was subsequently rewritten to follow the architecture outlined in Modern C++ Design: Generic Programming and Design Patterns Applied– Alexandrescu, chapter 5, "Generalized Functors".

This code uses:

• default template parameters to saves users from having to specify empty parameters when the number of parameters is smaller than the maximum supported number
• the pimpl idiom: the Callback class is passed around by value and delegates the crux of the work to its pimpl pointer.
• two pimpl implementations which derive from CallbackImpl FunctorCallbackImpl can be used with any functor-type while MemPtrCallbackImpl can be used with pointers to member functions.
• a reference list implementation to implement the Callback’s value semantics.

This code most notably departs from the Alexandrescu implementation in that it does not use type lists to specify and pass around the types of the callback arguments. Of course, it also does not use copy-destruction semantics and relies on a reference list rather than autoPtr to hold the pointer.

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