Cannot compare object.opEquals is not nogc

[Rufus Smith via Digitalmars-d-learn]

On Saturday, 23 July 2016 at 14:15:03 UTC, Lodovico Giaretta 
wrote:
> On Saturday, 23 July 2016 at 13:18:03 UTC, Rufus Smith wrote:
>> Trying to compare a *ptr value with a value in nogc code 
>> results in the error:
>>
>> Error: @nogc function '...' cannot call non- at nogc function 
>> 'object.opEquals'		
>>
>> Shouldn't object opEquals be marked?
>
> If object.opEquals is marked @nogc, than all D classes must 
> implement it as @nogc, because (of course) you cannot override 
> a @nogc method with a not- at nogc one (while the opposite is 
> possible, of course).
> So marking it @nogc is not only a big breaking change, but also 
> very limiting.

Um, this isn't right. GC code can always call non-gc code.

If you mark opEquals nogc, it breaks nothing except 
implementations of opEquals that use the GC. GC code can still 
call it nogc opequals, it only enforces opEquals code to avoid 
the GC itself, which isn't a terrible thing.

What is terrible is that nogc code can never have any equality 
comparisons! It is impossible unless one manually tests them, but 
how? Every method would be brittle. Do a memory test? compare 
element by element? One can't predict what to do.

So, you are trying off laziness to break nogc. As it stands, if 
nogc code can't compare equality, it is broken and useless. Why 
put it in the language then?

struct S(T)
{
    @nogc void test(T t1, T t2)
    {
       if (t1 == t2) return true;
       return false;
    }
}

Broke! Even if opEquals of T does not use any GC we can't write 
test to be nogc, which means we can't have S be nogc or anything 
that depends on S that is nogc. This must be a dirty trick played 
by the implementors of nogc to keep everyone on the gc nipple?

Equality comparison is more fundamental than the GC in 
programming. There is no fundamental reason why equality 
comparison depends on the GC.

All I can hope for now is that there is a robust way to compare 
that I can use that is marked nogc. Else all my nogc code is 
broke. I guess one has this problem with all opOp's!