Implementing typestate

[Ola Fosheim Grøstad via Digitalmars-d]

On Wednesday, 16 September 2015 at 17:03:14 UTC, Marc Schütz 
wrote:
> On Tuesday, 15 September 2015 at 21:44:25 UTC, Freddy wrote:
>> On Tuesday, 15 September 2015 at 17:45:45 UTC, Freddy wrote:
>>>  Rust style memory management in a library
>>
>> Wait nevermind about that part, it's harder than I thought.
>
> Yeah, I thought about type-states as a way of implementing 
> borrowing, too. I think the biggest difficulty is that the 
> state of one object (the owner) can be affected by what happens 
> in other objects (i.e., it becomes mutable again when those are 
> destroyed).

If the borrowed reference itself follows move semantics, can't 
you just require it to be swallowed by it's origin as the "close" 
operation?

pseudocode:

File<Open> f = open();
(File<OpenLending> f, FileRef<Ready> r) = f.borrow();

dostuff(r);

(File<Open> f, FileRef<Void> r) = f.unborrow(r);

File<Closed> f = f.close()