[swift-evolution] RFC: Preventing Retain Cycles (Memory Ownership Model)

[Joe Groff]

Rust attempted this sort of type-directed cycle prevention early in its development, when it was attempting to provide language-supported shared references without GC, and it didn't work out well for them in practice.

-Joe

> On Jul 29, 2016, at 6:42 PM, Andrew Bennett via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I'd like an opt-in way to verify and prevent unintentional strong references in Swift.
> 
> This can be used to verify ownership structures, and ultimately avoid retain cycles.
> 
> Read a draft proposal here:
> https://github.com/therealbnut/swift-evolution/blob/therealbnut-explicit-ownership/proposals/NNNN-explicit-ownership-type-attribute.md
> 
> TL;DR:
> 
> If you have any questions please read the proposal before asking here.
> 
> It's an opt-in attribute that defines a whitelist of types something can own. For example:
> 
> @owns(TypeA, TypeB) struct TypeC { ... }
> 
> I wrote this a few months ago, but we weren't accepting additive proposals. Now we're explicitly looking for something like this:
> 
> Memory ownership model: Adding an (opt-in) Cyclone/Rust inspired memory ownership model to Swift is highly desired by systems programmers and folks who want predictable and deterministic performance (for example, in real time audio processing code).  More pertinent to the goals of Swift 4, this feature is important because it fundamentally shapes the ABI.  It informs code generation for “inout", how low-level “addressors” work in the ABI, impacts the Swift runtime, and will have a significant impact on the type system and name mangling. 
> 
> - Chris
> 
> ----
> 
> Here's a link to the version of the proposal when I sent this email.
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