Flag proposal

[Andrei Alexandrescu]

On 6/10/11 3:36 PM, Nick Sabalausky wrote:
> "Nick Sabalausky"<a at a.a>  wrote in message
> news:istv62$2skn$1 at digitalmars.com...
>> "Andrei Alexandrescu"<SeeWebsiteForEmail at erdani.org>  wrote in message
>> news:isttf6$2oub$1 at digitalmars.com...
>>> On 6/10/11 1:52 PM, Robert Clipsham wrote:
>>>>
>>>> foo(param: true, otherParam: false);
>>>> foo(Flag!"param".yes, Flag!"otherParam".no);
>>>>
>>>> I don't know about you, but I find the former is far more legible. I'd
>>>> hate to see my code littered with Flag!"something".
>>>
>>> I agree it's more legible. The crucial question is whether the added
>>> legibility warrants adding a new feature to the language.
>>>
>>
>> I really see Flag more as a way to try to rationalize avoiding adding
>> named parameters to the language.
>>
>> And yes, the legibility of "foo(Flag!"param".yes, Flag!"otherParam".no);",
>> combined with the frequency of need for such a thing, and the complete
>> inability of Flag to address the problem for anything but bool, the
>> inability to document it separately (as Jonathan Davis pointed out), is
>> all definitely much much more than enough to warrant adding a
>> tried-and-proven feature that's become standard in damn near every other
>> modern language.
>>
>
> Regarding "the complete inability of Flag to address the problem for
> anything but bool", how are we going to wind up papering over that?
>
> Like:
>
> box(Int!"x"(3), Int!"y"(4), Int!"width"(100), Int!"height"(150),
> Int!"depth"(1), UInt!"color"(0xFFAA77));
>
> ?

I don't find it entirely fair to demean the suggestion as a tool to 
sustain your viewpoint.

Flag supporting only yes and no is not a "complete inability" - it is 
its charter. The plan is not to have Flag be a replacement for named 
arguments, but instead to have it support good practices for Boolean 
settings and replace a number of awkward enum definitions in Phobos.

As I mentioned, in the future it's possible to have Flag (or a related 
abstraction) support categorical features beyond yes and no, but it is 
not meant, and does not attempt, to cover named arguments.


Andrei