Eric Niebler wrote:
I recently had a C++ problem and found an answer that tickled my brain. In the spirit of Car Talk on NPR, I thought I'd share it in the form of a puzzler. <snip> Answer next week, unless someone beats me to it.
Wow, everybody loves a puzzle! This is good fun. Joaquin and Marco Co.: virtual inheritance. Clever! I think it instantiates O(N) templates though. Matus: This works but has scalability problems. To handle a set with N types, you need 2^N specializations of common_type_helper_picker. Giovalli: conditional operator. Wish I thought of that. But it requires types to be associated with integers via a global registry, so I can't use it. Is there a way to avoid select() and result<>? It's easy with typeof, but can you do it without? Marco Ce: This is pretty good! I think this instantiates O(1) templates in the case that a common type exists. Awesome. It's simpler that what I came up with, too. Steven W: Wow, makes my head hurt. I think I see what's going on -- 2^N specializations? Might not scale so well. Daniel Fey: Similar to what I came up with, but there's a trick that can (a) knock the 2^N overloads down to N, and (b) eliminate the need for typeof. -- Eric Niebler Boost Consulting www.boost-consulting.com