[boost] Re: call_traits

From: Edward Diener (eddielee_at_[hidden])
Date: 2004-07-05 19:23:07

David Abrahams wrote:
> "Edward Diener" <eddielee_at_[hidden]> writes:
>
>> What are the issues with call_traits which make it unusable ?
>
> As far as I can tell, there is no clear documentation of what
> _precisely_ any partcular member of call_traits<T> is for a given T.

The table given after "The following table shows the effect that call_traits
has on various types, the table assumes that the compiler supports partial
specialization: if it doesn't then all types behave in the same way as the
entry for "myclass", and call_traits can not be used with reference or array
types" seems to answer that pretty specifically. It gives the values which
call_traits will generate for any user defined type and various permutations
of a basic type.

> It's even less clear what fallback the library uses when a full
> implementation of call_traits would require partial specialization
> that isn't available.

See quote above. How many compilers without partial specialization, beside
VC6, does Boost really want to support anymore. My guess would be 0 and if
Boost didn't feel obliged to support VC6, I am sure all Boost developers
would be happier. I am not knocking the tremendous effort Boost has made to
support VC6, since I have used it myself and am appreciative of it. But if
call_traits doesn't largely work with VC6 in any meaningful way, I don't
think it is a reason to deprecate it.

>
> It seems as though the documentation is intended to be a more abstract
> description of what happens, but it leaves me (at least) feeling very
> unclear about what I'm actually getting.

Seems fairly clear to me. The only possibiliites not listed are other
permutations of user-defined types. I would think this latter may be a
documentation issue, but an educated guess would be that other permutations
of user-defined types would mirror the other permutations of basic types.

>
> It's also unclear to me what purpose is served by the "reference" and
> "const_reference" members.

In the beginning of the doc it specifies that both are for returning values
of reference and const reference respectively, while avoiding the reference
to reference problem.

I am not defending call_traits itself, which I have not used but which I am
thinking about using as part of my calling and returning style, but rather
the doc which seems fairly clear to me about what it is and does from a user
perspective.