[boost] [parameter] Possible breaking change

From: David Abrahams (dave_at_[hidden])
Date: 2006-02-12 10:11:34

As part of the new [un]named template parameter support, we are
considering a breaking change to the 

  binding<ArgumentPack, Keyword, Default = void> 

metafunction.  Right now, when no 3rd argument is supplied indicating
the default type, and the ArgumentPack contains no matching keyword,
the result is void.  Under the proposed change, the result would be a
compile-time error.  The upshot is that, to find out whether a
particular parameter is in the ArgumentPack, you'd need to supply some
tag type that you know won't appear in the ArgumentPack as the 3rd
argument to binding, and check for that.

Any objections?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com