On 16-05-2012 19:36, Steven Schveighoffer wrote:
On Wed, 16 May 2012 13:16:36 -0400, H. S. Teoh <[email protected]>
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
I guess we can conclude that one should not use 'null' or 'is' for
arrays unless absolutely necessary. '[]' and '==' should probably do for
the majority of code.
--
Alex Rønne Petersen
[email protected]
http://lycus.org
