https://github.com/swiftlang/swift/pull/85551/files

Preliminary support for existential in embedded Swift by aschwaigho...

Still missing is casting from existential to concrete type (the only we will initially support) and a bigger set of types (e.g foreign types).

12:26 AM

Embedded Swift で Existential を有効化するモードが実装されている

12:28 AM

/// The embedded swift_allocBox version is different to the standad one in that /// we want to avoid building metadata for the box type. Instead we store the /// metadata of the contained type in the heap object. To make this work when /// destroying the box the release needs to be special i.e `swift_releaseBox`. /// It does not call the the heap object metadata's destroy function. Rather, it /// knows that the allocBox's metadata is the contained objects and calls an /// appropriate implementation: `_swift_embedded_invoke_box_destroy`. /// Therefore, one cannot not use `swift_release` but rather must use /// `swift_releaseBox` to implement the "release" function of a box object.

12:28 AM

通常、alloc box はその box 専用の metatype を生成するけど、

12:28 AM

embedded existential ではその代わりに中身の型の metatype を持って、

12:29 AM

box を release するときに、そのモードを考慮するようにランタイム関数を拡張するっぽい

12:30 AM

つまりオーバーヘッドを減らしたから許容できるってことなんだろうかそれなら標準 Swift にも採用するべきな気がするが、box metatype が無いと困る場合もあるんだろうか・・・

12:31 AM

https://www.swift.org/blog/embedded-swift-improvements-coming-in-swift-6.3/ ブログも出たし、ownershipも進んでるし、なんだか色々やっている

Embedded Swift Improvements Coming in Swift 6.3

Embedded Swift is a subset of Swift that’s designed for low resource usage, making it capable of running on constrained environments like microcontrollers. Using a special compilation mode, Embedded Swift produces significantly smaller binaries than regular Swift. While a subset of the full language, the vast majority of the Swift language wor...