DIP 1021--Argument Ownership and Function Calls--Final Review

[Mike Franklin]

On Thursday, 19 September 2019 at 09:42:06 UTC, Walter Bright 
wrote:

> > [1]
> https://gist.github.com/PoignardAzur/9896ddb17b9f6d6f3d0fa5e6fe1a7088
>
> I haven't studied that. Is it a 100% solution? I know there's 
> one being worked on for C++, but it's an 80-90% solution.
>
> D needs to have a 100%, mechanically checkable, solution.
>
> We have 100% for transitive const and function purity. It's 
> hard to get code to pass, but worth it when one succeeds. The 
> Ownership/Borrowing solution is 100% which is what is appealing 
> about it.

There are two 100% solutions that I am aware of.  One is Rust's 
borrow checker, which I'm assuming is already familar to all, and 
the other is Pony's reference capabilities [1].  As the ownership 
and borrowing vision for D is being polished, I think it would be 
worthwhile to become familiar with Pony's model even if only to 
provide contrast and solidify existing ideas.

Graydon Hoare [2] and Niko Matsakis [3], both rock stars in the 
Rust community, provided some interesting commentary on Pony's 
model.

[1] - 
https://tutorial.ponylang.io/reference-capabilities/reference-capabilities.html
[2] - 
https://www.reddit.com/r/rust/comments/34rszb/pony_type_and_memory_safe_language/cqxkmm8/
[3] - 
https://www.reddit.com/r/rust/comments/34rszb/pony_type_and_memory_safe_language/cqxvxky/

I'm really excited about where you're going with all of this, but 
this DIP does seem like an odd thing to do in isolation from a 
complete ownership/borrowing model.  It still seems to me that a 
complete ownership/borrowing/reference-capabilities solution, in 
the general case, would already handle the use cases addressed by 
this DIP.

Mike