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

Andrew Bennett cacoyi at gmail.com
Fri Jul 29 20:42:11 CDT 2016

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:


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
> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160725/025676.html>


Here's a link to the version of the proposal
I sent this email.
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