How to enable custom "experimental" features in Swift?

Using Swift
1

Hey,

not sure where exactly to post this. I hope this is fine here.

I've been following the Observation Pitch with great interest and a first experimental implementation seems to have been merged into the main branch of Swift: https://github.com/apple/swift/pull/63725

I've never downloaded or used a development snapshot of Swift from the main branch before (from Swift.org - Download Swift) but I thought I'd give it a try.

I downloaded the snapshot from March 7, installed it and told Xcode to use it. That seems to work.

However, I can't figure out how to enable the experimental "Observation" feature. In the PR, I found the flag SWIFT_ENABLE_EXPERIMENTAL_OBSERVATION and from some other examples I found on the internet I figured that I'd need to add the following to my Swift Flags in Xcode:

-Xfrontend -enable-experimental-observation

Unfortunately, I get an error when I try to build the project:

<unknown>:0: error: unknown argument: '-enable-experimental-observation'

I've tried several variations of this, like -swift-enable-experimental-observation and -SWIFT_ENABLE_EXPERIMENTAL_OBSERVATION.

I'm not sure if I'm doing something wrong. Or is the feature not fully "public" yet?

I'd appreciate any help with this :slight_smile:

2

With the toolchain selected, I think you can

import Observation

to use these features. @Philippe_Hausler please correct me if that's wrong.

Doug

1 Like
3

That is correct; as of current I believe you need to still specify the enablement of the macro feature however.

1 Like
4

That should not be needed, either. Both SE-0382 and SE-0389 have been accepted, so all of the macro functionality used by Observation is enabled by default.

Doug

2 Likes
5

Are you using it on Lunux or Mac?

6

With the toolchain selected, I think you can

import Observation

Ah, thanks, didn't know that. Importing does work fine, without adding any kind of other Swift flags

Unfortunately, I can't use the @Observable macro. It gives me this error:

External macro implementation type 'ObservationMacros.ObservableMacro' could not be found for macro 'Observable'; the type must be public and provided via '-load-plugin-library'

I've seen the -load-plugin-library in the Macros Example Repository (that example project does build and works fine for me) and tried to copy over the Swift flags, including this -load-plugin-library, but it doesn't work. I don't really find anything on the internet about this flag.

Are you using it on Lunux or Mac?

I'm on a Mac.

1 Like