Jeff Law <l...@redhat.com> writes: > On 06/25/2015 03:49 AM, Richard Biener wrote: >> On Thu, Jun 25, 2015 at 5:19 AM, Jeff Law <l...@redhat.com> wrote: >>> On 06/24/2015 02:23 AM, Richard Sandiford wrote: >>>> >>>> Jeff Law <l...@redhat.com> writes: >>>>> >>>>> So I'm holding off on approving this one pending further discussion of >>>>> the use of multiple inheritance for nofree_ptr_hash. >>>> >>>> >>>> I thought that might be controversial. :-) My two main defences are: >>>> >>>> 1) This is multiple inheritance of traits classes, which all just have >>>> static member functions, rather than multiple inheritance of data- >>>> carrying classes. It's really just a union of two separate groups >>>> of functions. >>> >>> As I was thinking about this during review I almost convinced myself that >>> multiple inheritance from traits classes ought to be acceptable. >>> >>> As you state, they don't carry data and we're just getting a union of their >>> functions. One could probably even argue that traits classes by their >>> nature are designed to be composed with other traits and classes. >>> >>> I'm (obviously) not as well versed in this stuff as I ought to be, hence my >>> conservatism. It'd be real helpful if folks with more real world experience >>> in this space could chime in on the pros/cons if this approach. >>> >>> If we do go forward, ISTM updating our coding conventions to codify this >>> exception to the "avoid MI" would be wise. And my inclination is to go >>> forward, but let's give other folks a chance to chime in. >> >> Yes, I think this is ok. > Works for me. Richard S., as a follow-up can you update the coding > conventions, which I think it maintained in the ancient CVS repo for the > web pages (ping Gerald if you're unfamiliar with it).
OK, sounds good. How does this look? Thanks, Richard Index: htdocs/codingconventions.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/codingconventions.html,v retrieving revision 1.71 diff -u -r1.71 codingconventions.html --- htdocs/codingconventions.html 9 Jul 2014 00:03:05 -0000 1.71 +++ htdocs/codingconventions.html 25 Jun 2015 17:31:39 -0000 @@ -888,6 +888,9 @@ On the rare occasion that using mulitple inheritance is indeed useful, prepare design rationales in advance, and take special care to make documentation of the entire hierarchy clear. +(In particular, multiple inheritance can be an acceptable way of combining +"traits"-style classes that only contain static member functions. +Its use with data-carrying classes is more problematic.) </p> <p>
