Cannot compare object.opEquals is not nogc

[ag0aep6g via Digitalmars-d-learn]

On 07/31/2016 08:43 PM, Rufus Smith wrote:
> e.g., I have a nogc container and a remove(T obj). I can't search for
> obj and remove it because opEquals is not marked nogc. So I need an
> alternative that is somewhat robust.

Jonathan M Davis has already mentioned his plans to templatize 
object.opEquals, which would help here. In the meantime, you can make 
your own comparison function and use that instead of the == operator.

Note that you can add @nogc when overriding Object.opEquals, and you can 
call such a @nogc opEquals directly from @nogc code. You just can't use 
the == operator which is implemented in object.opEquals.

In code:

----
class C
{
     override bool opEquals(Object other) const @nogc { return false; }
}
void f(C a, C b) @nogc
{
     bool x = a == b; /* doesn't compile */
     bool y = a.opEquals(b); /* compiles just fine */
}
----

object.opEquals (i.e. the == operator) does a little more than just 
calling a.opEquals(b). You can check the source to see what it does exactly:

https://github.com/dlang/druntime/blob/master/src/object.d#L136-L156

You'd probably want to mirror that as closely as possible in a custom 
comparison function, so that the results are consistent with the == 
operator.

As far as I see, you can't do the typeid thing, though, because 
TypeInfo.opEquals is not @nogc. Ugh.