RFC: scope and borrowing

[via Digitalmars-d]

On Thursday, 28 August 2014 at 18:53:25 UTC, Jacob Carlborg wrote:
> On 2014-08-28 11:16, "Marc Schütz" <schuetzm at gmx.net>" wrote:
>
>> I'd rather introduce a special method that is called only by 
>> the GC.
>> Cleaning up after an object that goes out of scope has always 
>> been the
>> task of the regular destructor, it's undeterministic 
>> destruction that
>> needs special treatment.
>
> I was think about not breaking code. But introducing a new 
> function that is called by the GC which also calls the regular 
> destructor might work.

The other way round would be safer: A destructor automatically 
calls as its first step a finalizer (let's use that term for a 
destructor called by the GC) if present, but a finalizer doesn't 
call the destructor. Remember that the things that are forbidden 
in a finalizer are usually fine in normal destructors. By calling 
the destructor from inside the finalizer, you bring all the 
problems back that you wanted to get rid of by introducing a 
special finalizer, right?

And this would be backwards-compatible: There is already today no 
guarantee that a destructor gets called by the GC, so never 
calling it doesn't break any valid code, strictly speaking. Then 
you could place "safe" cleanup actions (like closing a file) into 
the finalizer, and "unsafe" ones (like removing yourself from a 
linked list) into the destructor, and you don't need to duplicate 
the actions from the finalizer in the destructor. The compiler 
might then even detect unsafe operations in the finalizer and 
refuse to compile them.