[swift-evolution] A case for postponing ABI stability

[Rahul Malik]

I agree that we shouldn't rush decisions but I feel like the emphasis of
ABI stability has been a factor in discussing a number of proposals for
Swift 4 and has been a core goal of this next major release. Seems strange
to deemphasize it and its importance at this time.

Below are some thoughts from my perspective as someone involved in the
decision to adopt Swift in production at work.

*ABI Stability*
The reality is that stability in the ABI is important for a number of
developers and companies considering adopting or that have already adopted
Swift. Shipping the runtime increases the binary size of every app that
ships with it and becomes a barrier in user acquisition due to the
increased app size. If I'm not mistaken this issue multiplies as you add
extensions to your application since they all bundle the runtime
separately. Due to these issues, ABI Stability is one of the leading
reasons we have not adopted Swift in our flagship app.

*API Stability*
This I would consider just as important as the ABI stability. Changing APIs
provides a lot of churn on developers that manage large codebases and I've
often heard of issues using the Swift migrator at scale which doesn't help.
I'd like to see a less drastic approach like Jonathan is suggesting where
we have clear indication of APIs that might change or at least allowing one
minor release where an API will warn if it's used but is still available to
allow developers time to migrate.

Right now I think it's important to keep ABI stability as a core tenant of
any proposal and acknowledge that we need to just flag how proposals will
affect ABI stability. This seems inline with our stance on the development
of a Rust-inspired `Memory Ownership Model`: "While a full memory ownership
model is likely too large for Swift 4 stage 1, we need a comprehensive
design to understand how it will change the ABI."

On Tue, Jan 24, 2017 at 3:16 AM, Georgios Moschovitis via swift-evolution <
swift-evolution at swift.org> wrote:

> > I'm not really sure if the String-changes affect the ABI, but none the
> less, I strongly agree with your opinion that things shouldn't be done in a
> hurry, and I hope that Swift keeps the courage to break things for the
> better (sporadically ;-)
>
> +1
>
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