[boost] Re: Non-standard feature proposed in help text of operators library??

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2003-07-22 09:18:47

Daniel Spangenberg wrote:
> No, I absolutely do understand, that  X<T> in the operators library defines
> operators which take T as an argument. I hope, that my explanation meant that
> (my english is bad, I know). But I think, that the standard does forbid the
> visibiliy
> of the operators injected by less_than_comparable<myclass> for myclass
> because myclass is not the associated with less_than_comparable<**>. Now the
> operators injected by less_than_comparable<myclass> take myclass as
> arguments (those with arguments, I mean) and should noot be visible for
> myclass.

They needn't be visible for myclass. They only need to be visible in the 
namespace where this happened. See 3.4.2/2:

"If T is a class type, its associated classes are the class itself and 
its direct and indirect base classes. Its associated namespaces are the 
namespaces in which its associated classes are defined."

The namespace is what is important here, not the class. The 
friend-operators declared by X<T> are injected to the namespace as given 
by 14.6.2/2:

"As with non-template classes, the names of namespace-scope friend 
functions of a class template special-ization are not visible during an 
ordinary lookup unless explicitly declared at namespace scope (11.4). 
Such names may be found under the rules for associated classes (3.4.2)."

note the "...namespace-scope friend functions...", which to me means 
that the operators are not injected to X<T>, but to the namespace where 
the explicit instantiation happened. As this should be the same 
namespace where T lives, anything should IMHO be legal C++. At least 
this is how I read the standard.

Regards, Daniel

PS: I don't think english is our problem, but if you feel more 
comfortable with german you can mail me directly if you like.

-- 
Daniel Frey
aixigo AG - financial training, research and technology
Schloß-Rahe-Straße 15, 52072 Aachen, Germany
fon: [phone], fax: [phone]
eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de