[boost] Re: is_convertible: rationale and wording

From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2003-01-30 13:37:42

On Thu, 30 Jan 2003 12:20:32 -0000, "John Maddock"
<jm_at_[hidden]> wrote:

>> I see that you haven't replied to this for long time now. So either
>> you are bored from the question, or it wasn't clear enough. To see if
>> it is the second case I thought to reformulate it:
>
>Well only for a day and a bit, sorry just busy :-(

Oops, I think I've to tune up my biological clock sorry :-) Maybe I
saw that you were replying in other threads but not in this one, or
maybe I was just eager to have a reply and thought it was long time
that I hadn't one. No intent to nag you, anyway.

>> Can you show, with an example, why the code used for named template
>> arguments can't reasonably use an expression?
>
>It doesn't have access to one, only a type: the usage is take some template
>parameter, see if it is convertible to some policy type, and if it is, then
>extract the policy information.
>
>John Maddock
>http://ourworld.compuserve.com/homepages/john_maddock/index.htm
>

The technique I know relies on detecting whether the template argument
is *derived* from some policy, and that's doable with expressions.
That's why I asked you what was the exact technique you were using.
Also, if you have any (other) example where "convertibility of a type"
is needed I would be glad to see it, because this is IMHO a crucial
point.

Genny.