Does D has C#'s string.Empty?

[Chris Cain via Digitalmars-d-learn]

On Friday, 26 September 2014 at 01:09:01 UTC, AsmMan wrote:
> On Friday, 26 September 2014 at 00:53:24 UTC, ketmar via 
> Digitalmars-d-learn wrote:
>> On Fri, 26 Sep 2014 00:24:27 +0000
>> AsmMan via Digitalmars-d-learn 
>> <digitalmars-d-learn at puremagic.com>
>> wrote:
>>
>>> It made me a bit confusing. How is the implementation of 
>>> string
>>> comparasion in D?
>> "" has length of 0. null has length of 0. two strings without 
>> content
>> are essentialy the same.
>
> but null has length? what's null in D?

To reinforce what ketmar is saying:

strings in D are just `immutable(char)[]` ... a simple array of 
immutable chars. All arrays are just (essentially) `struct Arr(T) 
{ T* ptr; size_t length; }` ... so this differs from C# where 
String is actually a class. So, when we talk about `string s = 
null;`, the structure would look like `ptr = null; length = 0`. 
You can still get the length out of a "nulled out string" (or any 
array type for that matter). Obviously in C#, that'd give you a 
null pointer exception since it's a class.

When you compare equality between two different arrays in D, 
you're checking for if they have all of the same elements (thus, 
ptr being different between two arrays is irrelevant). Trivially 
any two strings with length 0 are equal, so there are 4 billion 
equivalent empty strings in D (in 32-bit mode, and 2^64 in 64 bit 
mode, of course).

So, if you want an empty string, you can do any one of:

`s = null;`
`s.length = 0;`
`s = "";`

and you'll be fine.