[MLton-user] Feature request: MLton.Finalizable

[Matthew Fluet]

On Mon, 2 Jun 2008, John Reppy wrote:
> On Jun 2, 2008, at 7:05 PM, Matthew Fluet wrote:
>> On Mon, 2 Jun 2008, John Reppy wrote:
>> > The implementation is straightforward:
>> > 
>> >  fun cancelFinalizers (T{finalizers, ...}) = finalizers := []
>> > 
>> >  fun update (T{value, ...}, x) = value := x
>> > 
>> > Any chance of getting these added to MLton?
>> 
>> Your 'update' function doesn't work with the Finalizable implementation. 
>> The finalization functions are invoked on the original value v used to 
>> construct the finalizable value.  The closure passed off to the GC handler 
>> can't be closed over the reference cell pointed to by the weak pointer, 
>> else the reference cell would always be live.
>
> That's a more serious objection, since I'm trying to avoid the extra level of 
> indirection :(.

MLton can often flatten references into their containing structure.  Since 
the ref used by the weak pointer is not updated, it is a good candidate 
container.  So, while you may pay the indirection in the source code, the 
executable may not.