[Issue 2934] "".dup does not return empty string

[Steven Schveighoffer]

On Mon, 04 May 2009 16:56:49 -0400, Derek Parnell <derek at psych.ward> wrote:

> On Mon, 4 May 2009 17:44:56 +0000 (UTC), d-bugmail at puremagic.com wrote:
>
>> http://d.puremagic.com/issues/show_bug.cgi?id=2934
>>
>> schveiguy at yahoo.com changed:
>>
>>            What    |Removed                     |Added
>> ----------------------------------------------------------------------------
>>              Status|NEW                         |RESOLVED
>>          Resolution|                            |INVALID
>>
>> ------- Comment #2 from schveiguy at yahoo.com  2009-05-04 12:45 -------
>> From posts in the newsgroup, I've determined that this bug is invalid:
>>
>> 1. Duplicating an empty array should always return a null array.   
>> Otherwise,
>> you'd have to allocate space to store 0 data bytes in order for the  
>> result to
>> be non-null.
>>
>> 2. String literals have a null character implicitly appended to them by  
>> the
>> compiler.  This is done to ease calling c functions.  So a string  
>> literal's
>> pointer cannot be null, since it has to point to a static zero byte.
>>
>> The spec identifies specifically item 2 here:
>> http://www.digitalmars.com/d/1.0/arrays.html#strings
>>
>> see the section describing "C's printf and Strings"
>>
>> I could not find a reference for item 1, but I remember reading  
>> something about
>> it.  Regardless of it is identified specifically in the spec or not, it  
>> is not
>> a bug, as the alternative would be to allocate blocks for 0-sized  
>> arrays.
>
> Huh??? Duplicating something should give one a duplicate.
>
> I do not think that this is an invalid bug.
>
> Ok, so duplicating an empty array causes memory to be allocated - so  
> what!
> I asked for a duplicate so give me a duplicate, please.
>
> To me, the "no surprise" path is simple. Duplicating an empty array  
> should
> return an empty array. Duplicating a null array should return a null  
> array.
>
> Is that not intuitive?
>

what's not intuitive is comparing an array (which is a struct) to null.

char[] arr1 = "";
char[] arr2 = null;

assert(arr1 == arr2); // OK
assert(arr1 == null); // FAIL

I'd say that comparing an array to null should always succeed if the array  
is empty, but I guess some people may use the fact that the pointer is not  
null in an empty array.  I definitely don't want the runtime to allocate  
blocks of data when requested to allocate 0 bytes.

In any case, this bug is not valid, because the compiler acts as specified  
by the spec.

I never compare arrays to null if I can remember, I always check the  
length instead, which is consistent for both null and empty arrays.

-Steve