Thorsten Ottosen wrote:
"Daniel Frey" <daniel.frey@aixigo.de> wrote in message news:c2scpf$me8$1@sea.gmane.org... David Abrahams: [snip]
Why doesn't
T(pi)
Because T can have multiple ctors (taking i.e. float, double, long double and thus making the conversion ambiguous - I can't control that
from inside pi, the T is not exactly forwarded to pi's type when asked
for a conversion).
1. how big is this problem in practice?
Big AFAICT. Most UDTs that I saw have ctors to handle conversions from the built-in types. I would limit the useable types for no good reason. Also, the second problem I mentioned is even more serious - and solving it also solves the ctor-problem.
2.couldn't you just make a default choice? Let enable_if disable some if there is an ambiguity?
Not an option IMHO. A default is exactly what should be avoided at all cost. If someone uses quad-doubles or RWDecimal, he has a reason to do so. Silently injecting doubles (or any other default) could do a lot of damage and thus will work against the acceptance of the library. Safe use with no surprises is a lot more important than convenience and a default type isn't safe. BTW: These things are good to discuss. I think some of this should make it to the documentation :) Regards, Daniel -- Daniel Frey aixigo AG - financial solutions & technology Schloß-Rahe-Straße 15, 52072 Aachen, Germany fon: +49 (0)241 936737-42, fax: +49 (0)241 936737-99 eMail: daniel.frey@aixigo.de, web: http://www.aixigo.de