Relaxing the definition of isSomeString and isNarrowString

[Andrei Alexandrescu via Digitalmars-d]

On 8/24/14, 6:00 AM, "Marc Schütz" <schuetzm at gmx.net>" wrote:
> 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...

Yah, length should be there. I think ptr is good to require because I 
speculate many optimizations take advantage of the characters being 
contiguous.

Andrei