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Subject: Re: [boost] review request: addition to type_traits library of is_less_comparable<T, U> and others
From: Frédéric Bron (frederic.bron_at_[hidden])
Date: 2009-10-09 11:19:38

> Is it reasonable to additionally verify the returned type? IMO, such kind of
> traits should not make assumptions about the operators meaning, they should
> merely show whether the comparison expression is valid. Thus there also
> should not be a fails-to-compile case.

OK, what do you know if you know that you can write t<u but do not
know if it is convertible to bool?
You know that "t<u ;" is OK but maybe "if (t<u) ..." will not work ->
compile time error.
I think that in most cases you want to know that it behaves like
operator< used with built-in types.

Maybe it could be interesting for some people to have an additionnal
version just checking for existence but I am not convinced.

I agree that it is not "nice" to have a compile time error when used
with operator< returning void but I prefer that than returning true
because this behaviour is not the one expected by operator<. If
anybody has a solution on how to return false in such case...


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