----- Original Message ----- From: "Adam Merz" <adammerz@hotmail.com> To: <boost@lists.boost.org> Sent: Monday, August 16, 2010 7:23 AM Subject: Re: [boost][chrono] [dependence of common_type on Boost.TypeOf]
vicente.botet <vicente.botet <at> wanadoo.fr> writes:
----- Original Message ----- From: "Adam Merz" <adammerz <at> hotmail.com> To: <boost <at> lists.boost.org> Sent: Sunday, August 15, 2010 9:44 AM Subject: Re: [boost][chrono] [dependence of common_type on Boost.TypeOf]
vicente.botet <vicente.botet <at> wanadoo.fr> writes:
Hi again, I have reached to manage with the ambiguous overloads and all the tests works as before. I have do it as follows: <snip code>
That doesn't seem very robust in the case that there is no common type (in terms of the compiler error anyway).
Could you send the compiler error so we can talk of concrete things?
Thanks, Vicente
Really? You were just speaking of ambiguity errors yourself...
Okay then, two issues I see with a sizeof-based approach as you've shown it: First, it requires that both types be default constructable; otherwise, you get errors like the following (using MSVC10):
1>error C2512: 'Bar::Bar' : no appropriate default constructor available 1> see reference to class template instantiation 'common_type2<T1,T2>' being 1> compiled 1> with 1> [ 1> T1=Foo, 1> T2=Bar 1> ]
This can of course be worked around by working in terms of pointers to the provided types rather than the types themselves. Second, if there is no common type, you get potentially confusing ambiguity errors:
I will take care of this.
Or, if you make the aforementioned pointer changes, you get the even more confusing:
1>error C2446: ':' : no conversion from 'Baz *' to 'Foo *' 1> Types pointed to are unrelated; conversion requires reinterpret_cast, 1> C-style cast or function-style cast 1> see reference to class template instantiation 'common_type2<T1,T2>' being 1> compiled 1> with 1> [ 1> T1=Foo, 1> T2=Baz 1> ] 1>error C2070: ''unknown-type'': illegal sizeof operand
I find the message no so confusing: "Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast" and common_type2<T1,T2> appears also in the message. What others think? Best, Viecnte