CTFE bug causes null check to pass on null pointers (Issue 7602)

[Don Clugston]

On 21/03/12 11:22, Jens Mueller wrote:
> David Nadlinger wrote:
>> On Wednesday, 21 March 2012 at 09:51:43 UTC, Jens Mueller wrote:
>>> Interesting. How do I make use of this?
>>>
>>> […]
>>>
>>> What's the trick to use memory allocated in a CTFE. Say e.g. I
>>> want to
>>> build a tree at compile time using CTFE.
>>
>> You can't do that right now (i.e. converting CTFE-allocated memory
>> to initializers for run-time values), but it enables you to use
>> classes, etc. _during_ CTFE.
> 
> Just for clarification:
> Why do you say "initializers for _run-time_ values"? I believe I just
> want to allocate memory at compile-time.

Any heap-allocated object is on the CTFE heap. At runtime, it needs to
be on the runtime heap. There is currently no mechanism in the back-end
for transferring data from the CTFE heap to the runtime heap, so it
currently generates an error message.

You can return structs and arrays, because we have struct literals and
array literals, but there is no such thing as a class literal. CTFE will
currently allow you to return a class, but only if it is null.

> I just found out you are not allowed to return an instance. But you can
> use out parameters.

Oh dear. That sounds like a bug. There is just no way you can
automatically instantiate a class at runtime, using CTFE data. There
would need to be code in the runtime to do it, and it just doesn't exist!

That means I can achieve what I have in mind using
> classes. Even though it looks a bit clumsy and not like I do it in
> non-CTFE code.
> 
> Many Thanks.
> 
> Jens