[swift-dev] Disallowing weak struct properties

David Sweeris davesweeris at mac.com
Fri Jan 29 21:24:27 CST 2016

I'm against it, unless structs can have "WeakCollectionType" properties (which seems like it'd necessarily involve some of that compiler magic we're trying to avoid).

If reference/value semantics weren't tied to struct/class, I'd care a lot less.

I also wouldn't object to removing them from structs, but then adding a "strass" object classification for when you need weak inside a value-semantics object.

-Dave Sweeris

Sent from my iPhone

> On Jan 29, 2016, at 17:56, Jordan Rose via swift-dev <swift-dev at swift.org> wrote:
> Hi, everyone. What do you think about dropping support for 'weak' in struct properties? This would fix a semantic issue—'let' structs containing weak properties won't change out from under you—and (AFAICT) would make all values trivially movable, which is a great quality to have.
> This wouldn't change local variables, top-level variables, or class properties, just structs. It would make having an array of weak references a little harder, but honestly we should have proper weak-supporting collections anyway; as I understand it the behavior you usually want is auto-compacting rather than leaving a hole. (Evidence: Cocoa has NSHashTable for weak sets and NSMapTable for dictionaries with weak keys and/or values; there's no variant of NSArray that supports weak references other than by making a custom CFArray and being very very careful how you access it.)
> Anyway, thoughts? It's not really my department but it cleans up the same areas that are being affected by struct resilience.
> Jordan
> P.S. I know this would have to go through swift-evolution for real. I just want to know if it's a silly idea to begin with.
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