On Monday, 19 September 2016 at 20:21:30 UTC, Jonathan Marler
Yes that's why the template cannot deduce the parameters. The
question is, when the parameters cannot be deduced, and they
are all optional, would it be reasonable for the compiler to
infer that the user intended to use the default parameters?
This would be a destabilizing language-change and require even
more logic for templates.
I don't mind saying that any further complication of template
overload resolution is a rather unpleasant for me to think about.