Daniel Wallin <dalwan01@student.umu.se> writes:
David Abrahams wrote: [...]
The question is, what should we do about this? It turns out to be surprisingly hard to write the declarations of these temporary variables so they work in all cases. For example, v had to be a const& because in one case index_result<...>::type turned out to be
char const[4]
and when the default is used, it's
double
with p[value || ...] returning a double rvalue (by value).
Thoughts?
Make the user add reference to the Default type instead of index_result<>::type?
I don't fully understand what you're proposing or what it's supposed to address, but I think you might be missing the point. To make it safe to use, ideally index_result<...>::type whatever = p[x | some-expression]; would always cause a by-value return from p[...] when some-expression is an rvalue. By the same token, f( p[x | some-expression] ) should always return by-reference from p[...], for efficiency. This has a little less to do with how the user declares index_result<...>::type than with the result of indexing. -- Dave Abrahams Boost Consulting www.boost-consulting.com