Cannot compare object.opEquals is not nogc

[Marco Leise via Digitalmars-d-learn]

Am Sat, 23 Jul 2016 13:18:03 +0000
schrieb Rufus Smith <RufusSmith at indi.com>:

> 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?

The only situation that you can work around is if the 'object'
is actually known to be one of your @nogc objects. Then you
can simply downcast before calling opEquals.

It's certainly limiting, but just an artifact of OOP and I can
assure you that making D usable without GC has been high on
the priority list (for an community driven open-source project
anyways). Phobos got reworked to get rid of unnecessary GC
allocations and Andrei Alexandrescu contemplated making
object's methods @nogc at one point.

If you need a restricted object hierarchy, you'll have to
write a new "NoGcObject" base class. opEquals would still take
"object", though you can avoid a dynamic cast by writing:

  (cast(NoGcObject)cast(void*)obj).someMethod();

The cast to void* prior to the downcast drops the class type
information and a dynamic cast becomes a static cast.

-- 
Marco