Relaxing the definition of isSomeString and isNarrowString

[via Digitalmars-d]

On Sunday, 24 August 2014 at 01:06:31 UTC, Andrei Alexandrescu 
wrote:
> Currently char[], wchar[], dchar[] and qualified variants 
> fulfill the requirements of isSomeString. Also, char[], wchar[] 
> and qualified variants fulfill the requirements of 
> isNarrowString.
>
> Various algorithms in Phobos test for these traits to optimize 
> away UTF decoding where unnecessary.
>
> I'm thinking of relaxing the definitions to all types that 
> fulfill the following requirements:
>
> * are random access ranges
> * element type is some character
> * offer .ptr as a @system property that offers a pointer to the 
> first character
>
> This would allow us to generalize the notion of string and 
> offer optimizations for user-defined, not only built-in, 
> strings. Thoughts?

IMO in general it's a good proposal; I expected `isSomeString` to 
return `true` for higher-order ranges over strings, and was 
surprised that it didn't.

But `.ptr` must only be included if the elements are indeed 
contiguous in memory. For example, `std.algorithm.filter` applied 
to a string should not provide `.ptr`, but should IMO be treated 
as a string nevertheless.

Related: What about `.length`? RA ranges can also be infinite...