@ArrayBuilder in swift-collections?

[cal (Cal Stephens)]

Some good discussion in this pitch this week about introducing an official @ArrayBuilder implementation to the ecosystem:

Add @ArrayBuilder to the standard library

Hi everyone! We have leveraged @ArrayBuilder-like result builders at Airbnb for many years and have found it to really improve the ergonomics of constructing array values. This is such a common operation that it would be great to include a first-party solution for it in the standard library. Here’s a pitch, what do you think? Will call attention to the slightly orthogonal mini-pitch within this pitch: it would be great to support @ArrayBuilderattributes on properties and functions, rather than …

What’s the process for proposing additions to swift-collections? Is this in scope for the collections package?

Adding an @ArrayBuilder to swift-collections would still accomplish all of the goals from the pitch:

• Initializing array values is such a common operation that this addition will be relevant to many Swift projects.
• Including @ArrayBuilder in a core package like swift-collections enables it to become a standard best practice across the Swift ecosystem.
• Standardizing on a single, high-quality, optimized, official implementation reduces fragmentation and improves the quality of the overall ecosystem.

[lorentey (Karoy Lorentey)]

I have two potential issues:

• My biggest worry is the prospect of adding a macro target or a dependency to swift-collections. (People are using this package in a variety of weird/unsupported ways, and the slightest deviation from the basic build setup will cause problems.)

• Second, the feature should probably be more flexible -- it should allow creating instances other than an Array. Perhaps this feature should be integrated into the design work for the generalization of ExpressibleByArrayLiteral?