Re: [boost] [range] as_literal always returning iterator_range

Subject: Re: [boost] [range] as_literal always returning iterator_range
From: Jeremy Maitin-Shepard (jeremy_at_[hidden])
Date: 2011-05-04 10:59:55

On 05/03/2011 05:22 AM, Tobias Germer wrote:
> Hi all,
>
> I think there is a problem with the behavior of boost::as_literal. If I
> got it right, it is supposed to create an iterator_range from
> null-terminated strings, which is fine. However, it also creates
> iterator_ranges from exisiting ranges, i.e., it converts general ranges
> to iterator_ranges. I think as_literal should fall back to identity
> (i.e., just return its argument) if its argument is already a range.
>
> With the current behavior, the type information of the range is lost.
> This is a problem if I write generic code and want to dispatch several
> cases based on the type of the range. Consider the following example:
>
> -------------------------------
> template<class Rng>  void f( Rng const&  r ) {...}
> template<class T>  void f( iterator_range<T*>  const&  r ) {...}
> void f( std::string const&  s ) {...}
> void f( std::vector const&  v ) {...}
>
> template<class Rng>
> void g( Rng const&  r ) {
> 	f(as_literal(r));
> 	...
> }
>
> -------------------------------
>
> Function g() accepts general ranges as well as zero-terminated strings.
> It dispatches its argument using the type of the range and the overloads
> of f(), in order to execute special code for some ranges like strings
> and vectors. (In my particular case, I have special treatment for ranges
> of contiguous memory.)

Note that at least in your case, it seems there should be a more direct 
way to achieve what you want, e.g. an iterator/range trait to determine 
if an iterator can be handled like a pointer to contiguous memory.