Relaxing the definition of isSomeString and isNarrowString

[Andrei Alexandrescu via Digitalmars-d]

On 8/24/14, 6:16 AM, Dmitry Olshansky wrote:
> 24-Aug-2014 16:24, Andrei Alexandrescu пишет:
>> (Speaking of which: Some, but not all, types in std.container use
>> reference counting. One other great area of improvement would be to
>> guarantee that everything is std.container is reference counted.
>> Containers are the perfect candidate for reference counting - they are
>> typically large enough to make the reference counting overhead
>> negligible by comparison with the typical work on them.)
>>
>
> The rest of post is mostly in line with my reasoning (except for nobody
> measures stuff, it's just bullshit).

Apologies for that, thanks for setting me straight.

> Speaking of data-structures I find just about the opposite. Most data
> structure are small, which must be the fact so fondly used by C++
> vector: small-string optimization. Only very few data-structures are
> large in a given program, and usually correspond to some global tables
> and repositories. Others are either short lived byproduct of input
> processing or are small data-sets attached to some global entity.

I don't know of any std::vector that uses the small string optimization. 
std::string does ubiquitously because (a) strings are often handled as 
values, and (b) C++11 put refcounted strings into illegality (forced 
mistake) therefore robbing implementers of an important optimization.

In a way both C++ and D got it "wrong". Arrays/containers are entity 
types - they have identity and should be manipulated most often by 
reference. Presence of pass-by-value of containers in C++ programs, save 
for rvalue optimization purposes, is suspicious. In contrast, strings 
are value types - they are handled most often as a unit and passed by 
value, just like e.g. numbers.

C++ made both containers and strings value types, so it needs forever to 
look over its shoulder about n00bs copying large containers unwittingly. 
It also does a fair amount of unneeded string copying, and optimizing 
string-based C++ code is nontrivial. D made both arrays and strings 
slices, a data structure made highly expressive by the garbage collector 
but that occasionally confuses people. With std.refcounted.RCString and 
std.container.Array we get both abstractions "right".


Andrei