AMDG On 08/15/2015 10:00 AM, Nat Goodspeed wrote:

The code with which I'm working has two similar template classes: they have a common subset of 8 methods that could be used on an instance of either. For performance reasons, these methods are not virtual. As far as the compiler knows, the two template classes are unrelated.

Naturally we can write a template function to accept an instance of either template class, as long as it uses only methods from the common subset.

I also want to support runtime polymorphism, permitting a non-template function to accept an instance of either template class. Obviously that will incur some performance hit, but the coder can decide whether or not his/her function is performance-critical. If so, s/he can write that function to accept one or the other specific template class -- or write a template function.

We want to incur the performance hit only when the coder deems that an acceptable tradeoff. The classic solution would be to derive both template classes from a common base class and make the common methods virtual -- but then that penalizes every consumer.

I haven't yet used Boost.TypeErasure, but it seems to me potentially applicable to this problem.

I see the example[0] illustrating use of BOOST_TYPE_ERASURE_MEMBER(). I was going to define requirements for each of the 8 common methods ... but then I became confused. Our common methods use a template parameter from the parent template class as a method parameter type. Can I invoke BOOST_TYPE_ERASURE_MEMBER in a generic way that would support all valid template parameters?

Two of the 8 common methods are template methods, accepting a parameter whose type is a template parameter for the method rather than the containing class. I don't know whether that introduces further complexity.

So, your interface looks something like this: template<class T> class A { public: void f(); void g(T); template<class U> void h(U); }; To handle g, you need to treat T as an associated type. http://www.boost.org/doc/html/boost_typeerasure/multi.html http://www.boost.org/doc/html/boost_typeerasure/concept.html#boost_typeerasu... In order to handle the template h, you need to type erase U like this: has_h<void(any<whatever_the_requirements_for_U_are>)> In Christ, Steven Watanabe