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digitalmars.D.bugs - [Issue 5171] New: disable doesn't work on opEquals functions

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5171

           Summary:  disable doesn't work on opEquals functions
           Product: D
           Version: D2
          Platform: Other
               URL: http://www.digitalmars.com/d/2.0/attribute.html#disabl
                    e
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: Jesse.K.Phillips+D gmail.com
                CC: Jesse.K.Phillips+D gmail.com



10:15:28 PDT ---
When overriding a function of a base class  disable does not cause compile time
errors when called.

class A {
     disable override equals_t opEquals(Object other) {
        return false;
    }
}

void main() {
    auto a = new A();
    auto b = new A();

    if(a == b)
        assert(0);
}

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Nov 05 2010
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5171


Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |schveiguy yahoo.com
         Resolution|                            |INVALID



11:00:33 PDT ---
This isn't actually possible.  What I would suggest is the compiler failing to
compile your class instead, because you can't disable a base function.

If for example, you have a function like this:

bool foo(Object o1, Object o2) {...}

Then would it be safe to assume that you could pass both a and b to foo?  If
so, then isn't it possible for foo to call o1 == o2?  And how could the
compiler possibly statically disable this?

I'm going to mark it as invalid, and if you think you'd rather have the
behavior where  disable doesn't compile on overridden functions, then you can
reopen with that description.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5171


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc





 This isn't actually possible.  What I would suggest is the compiler failing to
 compile your class instead, because you can't disable a base function.


I agree. Where possible a good compiler has to statically disallow impossible
code :-)

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5171




Added a note to bug 3934

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prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5171


Jesse Phillips <Jesse.K.Phillips+D gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |
            Summary| disable doesn't work on    |Prevent compiling of class
                   |opEquals functions          |when  disable is used on an
                   |                            |overriding function
           Severity|normal                      |enhancement



11:10:36 PST ---
class A {
   void hello() {
   }
}
class B : A {
    disable override void hello() {
   }
}

void main() {
   auto a = new A();
   A b = new B();

   b.hello();
}

The compiler should not compile the class saying something to the effect of:
Can not disable method hello in base class A from B.
Or another suggestion "Cannot  disable overriding function hello in B"

Note that I think the code below should still compile:

class A {
    disable void hello() {
   }
}
class B : A {
   override void hello() {
   }
}

void main() {
   auto a = new A();
   B b = new B();

   b.hello();
}

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Nov 09 2010