[boost] Re: Formal Review: FOREACH macro

From: Eric Niebler (eric_at_[hidden])
Date: 2005-05-11 12:08:14

Peter Dimov wrote:
> 
> It would be perfectly reasonable for a language-level foreach to omit 
> the trailing zero when iterating over a character literal. But I don't 
> think that this case is possible to detect. I wouldn't be surprised if 
> it is, though, given the current wizardry in BOOST_FOREACH (somehow 
> exploiting the fact that literals are const but convertible to char*.)
> 

It does? What makes you think that?

I wonder if the fact that a const char[N] is convertible to a 
(non-const) char* can be used to detect whether a given character array 
should be treated as a null-terminated string. It's an interesting 
question, but I don't think it's a good idea, becuase it wouldn't handle 
cases like:

   const char sz[] = "hello";
   boost::size(sz); // 5 or 6?

   boost::size("hello"); // better give the same answer as above

FWIW, I agree with Peter and Dave A. that character arrays should be 
treated as arrays and not as null-terminated strings. The truth is, you 
just don't know, and you need the user's guidance to pick.

I'd like to see something like:

template<typename T, std::size_t N>
iterator_range<T const *>
ignore_trailing_null(T const (&rg)[N])
{
   BOOST_ASSERT(T(0) == rg[N-1]);
   return make_iterator_range(&rg[0], &rg[N-1]);
}

That way:
   boost::size("hello"); // 6
   boost::size(ignore_trailing_null("hello")); // 5

Perhaps there is a better is a better name than "ignore_trailing_null".

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com