Sets / associative arrays with void values?

[Carlos Santander]

Chris Nicholson-Sauls escribió:
> Jeff M wrote:
>> On 2007-01-06 16:05:06 -0800, "Vladimir Panteleev" 
>> <tehcybershadow at gmail.com> said:
>>
>>> I've been wondering whether D supported sets, or something similar. 
>>> What I  have in mind isn't unlike associative arrays, but without 
>>> values: an  unordered list with quick look-up and simple 
>>> addition/removal of elements,  yet still capable of enumeration, etc.
>>>
>>> I followed my intuition and tried to declare an associative array 
>>> with a  "void" value type:
>>>
>>> void[int] foo;
>>>
>>> To my surprise, it compiled. And even the "in" operation and the 
>>> .keys and  .values properties worked fine (or as fine as they can 
>>> work with an empty  associative array).
>>>
>>> Of course, the question comes: how would one add keys to such a 
>>> construct?  The practical answer is obvious: use a real "dummy" data 
>>> type (bit, for  example) as the value type, but I find it a shame 
>>> that declaring such  constructs is allowed - yet you can't really use 
>>> them.
>>
>> It would be nice if a "void[int]" array was usable. Associative arrays 
>> are create-on-access, so "foo[5];" should be a legal for creating an 
>> index in the array, but this throws an error.
>>
>> -- Jeff
>>
> 
> Actually I'm pretty sure create-on-access was removed several releases 
> back?  And I also thought the compiler no longer allowed a void value 
> type for associative arrays, but I guess I was wrong on that one.
> 
> -- Chris Nicholson-Sauls

That's true.
Back then, I used "void[T]" as a set, but since the change, I use "T[T]".
BTW, since "void[T]" is mostly useless (for the reasons stated above), would it 
be reasonable for the compiler to flag such a declaration as an error?

-- 
Carlos Santander Bernal