"".dup is null

[Georg Wrede]

Steven Schveighoffer wrote:
> On Mon, 04 May 2009 10:22:49 -0400, Qian Xu 
> <quian.xu at stud.tu-ilmenau.de> wrote:
> 
>> Steven Schveighoffer wrote:
>>
>>> I think you might have a bug?
>>>
>>> "".dup is the same as s.dup, not sure why you would expect it to be
>>> not-null.
>>>
>>> -Steve
>>
>> If I have not explained clearly.
>> Here is the full code:
>>
>>   char[] s;
>>   assert(s     is null);
>>   assert(s.dup is null);
>>
>>   assert(""     !is null); // OK
>>   assert("".dup !is null); // FAILED
>>
>> At least the last two lines behave not consistent.
>> Either both are failed, or both are passed.
> 
> 
> OK, your original post was this:
> 
>   assert( s.dup  is null); // OK
>   assert("".dup !is null); // FAILED
> 
> 
> The compiler always returns a null array if you dup an empty array.  The 
> reason being: why allocate memory for something that is zero length?
> 
> If anything, the oddity is this line:
> 
> assert("" !is null);

If I remember correctly, string literals are stored with a null 
appended, so as to make them easier to use with OS calls, etc. Could it 
be that "" stores a 1-byte string, consisting with just this null? Then 
this behavior would be understandable.

> But of course, no memory is allocated for literals, so at least needless 
> memory allocation does not occur.
> 
> To be consistent, I think assert("" is null); should pass, but it's a 
> minor inconsistency at best.
> 
> I usually never compare arrays to null for this reason...
> 
> -Steve