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digitalmars.D.bugs - [Issue 346] New: 'is' operator inconsistant with arrays

reply d-bugmail puremagic.com writes:
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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Sep 12 2006
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=346


bugzilla digitalmars.com changed:

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





"==" 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.


--
Sep 12 2006
prev sibling next sibling parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
<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.
Sep 12 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=346






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.


--
Sep 12 2006
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=346








 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.


--
Sep 12 2006