Thoughts on replacement languages (Reddit + D)

[aldanor via Digitalmars-d]

On Monday, 12 January 2015 at 11:04:45 UTC, francesco.cattoglio 
wrote:
> On Sunday, 11 January 2015 at 19:30:59 UTC, ponce wrote:
>
>> When does invalidMemoryOperationError happen and how do you 
>> avoid it?
>
> Typical example:
> using (a slightly outdated version of) gfm library, I have  few 
> gfm objects lying around on which I forget to call a close() 
> function. When the GC collects them the destructor runs 
> close(), which in turn calls for some allocation (e.g: 
> allocates for a string to send to the logger), 
> invalidMemoryOperationError pops up.
> This usually only happens at the end of execution, sometimes 
> however it happens randomly during program execution due to the 
> randomness of GC operations.
> The only way out of this is manually closing everything 
> correctly. I.e: I'm almost back to C++ manual memory 
> management. Catching the exception is an unsatisfactory 
> solution because I would still be leaking resources[1]. If 
> possible, things are made even worse in that RefCounted doesn't 
> work for classes, but that you can work around that (class 
> instance into refcounted struct, not really elegant and 
> requires lots of discipline, since it's easy to escape an extra 
> reference).
>
> [1] For everyone who doesn't know: non trivial destructors are 
> really useful in gfm because it wraps some C libraries, and 
> cleaning up C allocated resources is usually important. Proper 
> execution of gfm's close() for every class would be ideal.
Sounds like an exact same problem I have run into recently: class 
wrappers around HDF5 C library need to do something not @nogc in 
a destructor and also have to call the C-level releasing 
functions. Can't do that in a destructor since then you get the 
invalidMemoryOperationError; can't make classes structs and use 
refcounted since there's an implied type hierarchy which becomes 
a mess with alias this... the only way is to put that in close() 
and then not forget to call it manually.

Wish there was a standardized way of running non- at nogc user code 
before the dtor actually runs (and anytime after it's known to be 
guaranteed to run).