Re: [boost] whitespace and user-defined types in lexical_cast

From: Alexander Nasonov (alnsn_at_[hidden])
Date: 2007-02-01 07:42:55

30.01.07, 21:03, John Salmon <john_at_[hidden]>:
> The patch satisfies that test on my system (Linux, gcc-3.3.3).  I was
> surprised that such a test was not already in the regression suite.
> Something like it obviously should be, so I added some very similar
> tests just to be sure.  These are in the original patch:

Thanks. I'll add them.

> Yes.  There have been a few discussions over the years.  There are two
> basic themes:
> 1 - somebody thinks that lexical_cast ought to work on a type whose
> operator>> isn't smart enough to handle a non-default skipws flag.
> The response is typically "your operator>> is broken", followed by
> more or less discussion about whether lexical_cast should accommodate
> "broken" operator>> anyway.  We are repeating this theme.
> 2 - a desire for consistency between the handling of leading
> whitespace and trailing whitespace.
> I would suggest that the fact that questions of type 1 keep coming up
> is an indication that the current behavior is surprising and
> alternatives should be explored.  If we can change it so that it is
> less surprising to "newbies" without breaking anything else and
> without introducing new complexity, I think we should.
OK.

> I would suggest that the answer to questions of type 2 is to observe
> that it's not trailing whitespace that causes the exception, it's
> trailing *anything*.  As such, it should be clearly documented.  In
> fact, the proposed text for the specification of lexical_cast in TR2
> makes this very clear.
I'll make sure it's documented in boost.

> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1973.html
Thanks for reminding me of this text. I found few inconsistencies with the boost documentation.
-- 
Alexander Nasonov