While porting Yomm11 to the D language, I had a few fresh ideas, some of which are relevant to the C++ library. In addition, my colleague David Goffredo educated me on the power of the preprocessor's variadic macros. This prompted me to completely rewrite yomm11. Here are the improvements:
Yomm11 method dispatch is very fast, provided that you instrument all the classes that partake in method calls. This means adding macro calls inside classes, and sometimes adding constructors. The purpose is to add a pointer to a method table, which plays a role very similar to the virtual function table created by the compiler.
As an alternative, yomm11 supports an orthogonal mode: the method table pointer is stored in a global map indexed by the type_index of the virtual arguments. No modification to existing classes is required, but method dispatch is much slower (roughly by a factor of 10).
Yomm2 does away with class instrumentation. Classes need to be registered but need not be modified. The method pointer is acquired from a collision free global map indexed by a perfect integer hash of the address of the type_info object found in the argument's virtual table. See the implementation notes for more details. As a result, calling a method with one virtual argument is only 10-15% slower than calling the equivalent virtual member function.
In yomm11, methods are called via a function object created by the
MULTI_METHOD macro. Consequently, methods cannot be overloaded, because this
would create two objects with the same name.
In Yomm2, declaring a method creates a plain inline function. Thus it is possible to create several methods that have the same name and differ only by their signature. It is also possible to take a pointer to a method.
Yomm2 allows virtual arguments of std::shared_ptr type, in addition to
ordinary pointers and references. It is possible to add support for other
pointer types by specializing yorel::yomm2::virtual_traits.
Yomm11 uses a template (declared by MULTI_METHOD) to contain the method's
specialization. They are now created in hidden namespaces.