The more interesting question

[Steven Schveighoffer]

On Wed, 16 May 2012 13:16:36 -0400, H. S. Teoh <hsteoh at quickfur.ath.cx>  
wrote:

> On Wed, May 16, 2012 at 01:07:54PM -0400, Steven Schveighoffer wrote:
> [...]
>> For example:
>>
>> auto str = "abcabc";
>> assert(str[0..3] == str[3..$]); // pass
>> assert(str[0..3] is str[3..$]); // fail
>>
>> which is very counterintuitive.
> [...]
>
> I don't find that counterintuitive at all. To me, 'is' concerns memory
> identity: are the two things actually one and the same _in memory_? (In
> this case, no, because they are different chunks of memory that just
> happens to contain the same values.) Whereas '==' concerns logical
> identity: do the two things represent the same logical entity? (In this
> case, yes, these two arrays contain exactly the same elements.)
>
> I'd argue that 99% of the time, what you want is logical identity (i.e.,
> ==), not memory identity.

What's counter intuitive is if you use null as a 'special marker', then  
you use == in most cases, but that one case where you want to 'check for  
the special marker', in which case you *have* to use is.

-Steve