Variadic template aliases as template arguments (part 2)
This is a follow-up of another question. It refers to the same problem (I hope) but uses an entirely different example to illustrate it. The reason is that in the previous examp
-
This does not answer the question whether the code above is valid, but is a quite pretty workaround that I have found by experimenting shortly after asking the question, and I think is useful to share.
All that is needed are the following definitions:
template class F> struct temp { }; templateclass F> F subs_fun(temp ); template class F, typename... A> using subs = decltype(subs_fun (temp ())); then, wherever
Fwould be problematic, replace it withsubs. That's it. I cannot explain why, but it has worked in all cases so far.For instance, in the SFINAE example of the question, just replace line
templatestatic pass > _(int); by
templatestatic pass > _(int); This is a change at one point only, all remaining code stays the same. You don't need to redefine or wrap every template metafunction that with be used as
F. Here's a live example.If
Fis indeed valid and compilers support it eventually, it is again easy to switch back because changes are minimal.I find this important because it allows specifying a SFINAE test in just two lines
templateusing type_of = typename T::type; template using has_type = sfinae and is completely generic. Typically, each such test needs at least 10 lines of code and implementations of
加载中...
- 热议问题