On 6 May 2016 at 20:51, Marc Glisse <marc.gli...@inria.fr> wrote: > Hi Ville, > > since you wrote the latest patches on tuple constructors, do you have an > opinion on this patch, or alternate strategies to achieve the same goal? > > https://gcc.gnu.org/ml/libstdc++/2016-04/msg00041.html
I have fairly mixed feelings about the approach; it's adding a tag type and more enable_ifs into the base classes of tuple, which I'd rather not do unless absolutely necessary. Then again, the testcase you add looks like something we want to support properly. I haven't analyzed your patch in a very detailed manner; my initial thought was "can't we do this in the constraints of tuple's constructors", but looking at the patch and knowing the constructors of tuple, I don't think we can. I think the patch is ok, but I think it would be a good idea to have a comment on the added tag type and its purpose. Minor point: the technique that looks like typename enable_if< !is_same<_UHead, _Head>::value, bool>::type = false isn't necessary unless we have another overload that we need to distinguish with true/false. For a single overload, just using typename = typename enable_if< !is_same<_UHead, _Head>::value, bool>::type works equally well. The amount of boilerplate is more or less the same, so that's really not a significant matter, just an fyi. :)
