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digitalmars.D.bugs - [Issue 2347] New: opIs is missing

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2347

           Summary: opIs is missing
           Product: D
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: andrei metalanguage.com


The "is" operator is defined for built-in references and for slices. However,
user-defined smart references and slices want to define it as well to integrate
properly with built-in slices.

The definition of opIs should follow that of opIn.


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Sep 07 2008
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2347


smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg iname.com





I think that having opIs is philosophically wrong.  The whole point of is is to
override any type-defined equality operator by forcing a byte-for-byte
comparison.  There are probably plenty of template libraries and the like that
rely on this.

What are these "user-defined smart references", anyway?


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Sep 09 2008
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2347






An example of "user-defined smart references" would be a ScopePtr!(T) that
destroys an object when it goes out of the scope. Some reference-counted smart
pointer also behaves just like an ordinary point and one would like to be able
to compare SmartPtr against null using "is null" syntax:

auto ptr = SmartPtr!(MyClass)(new MyClass());
assert(ptr !is null);


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Sep 10 2008
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2347








 auto ptr = SmartPtr!(MyClass)(new MyClass());
 assert(ptr !is null);


Hang on ... is this a smart _pointer_ or a smart _reference_?

If a pointer, it makes no sense to use is to compare them as pointing to the
same object.  And even if it's a reference, what practical use is there in
being able to use is for this?  ISTM it would break more generic programming
cases than it would open up.


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Sep 10 2008