http://d.puremagic.com/issues/show_bug.cgi?id=5256

           Summary: null Rebindable testing not supported
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-11-21 18:55:50 PST ---
This D2 program shows that you can't test if a class reference wrapped with Rebindable is null:


import std.typecons;
const class Foo {}
void main() {
    auto a = Rebindable!Foo(new Foo);
    a = new Foo;
    assert(a !is null); // err
}


DMD 2.050 generates:
test.d(6): Error: incompatible types for ((a) !is (null)):
'Rebindable!(const(Foo))' and 'void*'


Is this the currently correct way to do it? (It works):

assert(a.get() !is null); // OK

I have seen the get() method is not documented on the site, so is that a temporary limitation caused by the unfinished "alis this" implementation?

(Issue tagged with "Component: DMD" because I think it's a limit of "alias
this").

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Andrei Alexandrescu <andrei@metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei@metalanguage.com
         AssignedTo|nobody@puremagic.com        |andrei@metalanguage.com


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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |DUPLICATE


--- Comment #1 from bearophile_hugs@eml.cc 2011-07-30 11:03:08 PDT ---
assert(a !is null); is wrong code.

Bug 4773 is now fixed. Now you are allowed to write:


import std.stdio, std.typecons;
const class Foo {
    invariant() { writeln("*"); }
}
void main() {
    auto a = Rebindable!Foo(new Foo);
    a = new Foo;
    //assert(a); // calls Foo.invariant()
    //assert(cast(bool)a); // doesn't call Foo.invariant();
    auto f = new Foo();
    assert(f); // calls Foo.invariant()
    assert(cast(bool)f); // doesn't call Foo.invariant();
}


So I consider this bug too fixed.

*** This issue has been marked as a duplicate of issue 4773 ***

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