http://d.puremagic.com/issues/show_bug.cgi?id=346

           Summary: 'is' operator inconsistant with arrays
           Product: D
           Version: 0.166
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P3
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: ibisbasenji@gmail.com


It has been my understanding that the 'is' operator, when working with types other than objects, is an alias for the '==' operator.  (For template simplicity, as I recall.)  However, the following code illustrates a case where it is different in behavior.  (My apologies if this is not really a bug, but I don't know what else to call it.)

--------------------------------------------------
import std .stdio ;

void main () {
  static int[] foo = [1, 2, 3] ,
               bar = [1, 2, 3] ;

  int[] def = foo;

  if (foo == bar) writefln(" foo == bar");
  if (foo is bar) writefln(" foo is bar");

  if (foo == def) writefln(" foo == def");
  if (foo is def) writefln(" foo is def");
}

--------------------------------------------------
Outputs:
 foo == bar
 foo == def
 foo is def


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http://d.puremagic.com/issues/show_bug.cgi?id=346


bugzilla@digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #1 from bugzilla@digitalmars.com  2006-09-12 23:48 -------
"==" means the contents of the array are the same. "is" means the arrays occupy the same location in memory. The program is behaving as expected.


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<d-bugmail@puremagic.com> wrote in message news:bug-346-3@http.d.puremagic.com/issues/...
> http://d.puremagic.com/issues/show_bug.cgi?id=346

> It has been my understanding that the 'is' operator, when working with
> types
> other than objects, is an alias for the '==' operator.  (For template
> simplicity, as I recall.)  However, the following code illustrates a case
> where
> it is different in behavior.  (My apologies if this is not really a bug,
> but I
> don't know what else to call it.)

I'd say that this is proper, but just a fuzzy area.  == compares the values of the arrays, and 'is' sees if the array references refer to the same data. The same way as class instances: == compares the values (using opEquals), and 'is' sees if they point to the same instance.

http://d.puremagic.com/issues/show_bug.cgi?id=346





------- Comment #2 from ibisbasenji@gmail.com  2006-09-13 00:02 -------
Fair enough, and that does make sense.  Although, having experimented a little further, I see that 'is' is using the .ptr of the arrays (logical).  This means that any slice which begins at index 0 will also match true to an 'is'.  Much to be considered when writing templates with arrays in mind.


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http://d.puremagic.com/issues/show_bug.cgi?id=346





------- Comment #3 from ibisbasenji@gmail.com  2006-09-13 00:04 -------
(In reply to comment #2)
> Fair enough, and that does make sense.  Although, having experimented a little further, I see that 'is' is using the .ptr of the arrays (logical).  This means that any slice which begins at index 0 will also match true to an 'is'.  Much to be considered when writing templates with arrays in mind.
> 

Gah, no, I retract that.  It does check the other properties, just in case. This is good.  :)  I can work with that.


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