> On Jul 29, 2016, at 5:20 PM, Jacob Bandes-Storch via swift-evolution
> <swift-evolut...@swift.org> wrote:
>
> Chris writes:
> - Source stability features: These should be relatively small, but important.
> For example, we need a “-std=swift3” sort of compiler flag. We may also add
> a way to conditionally enable larger efforts that are under development but
> not yet stable - in order to make it easier to experiment with them.
>
>
> I am curious whether the team has thoughts on how to organize the compiler
> codebase in such a way that new features can be added, and possibly
> source-breaking changes made, while still keeping the old functionality
> around.
>
> Are any obvious areas that will need refactoring to make this feasible?
> (Perhaps they could be turned into StarterBugs.)
I think this would be a great thing to do. We need a few things:
- The actual compiler flag. It is worth bikeshedding how it is spelled.
“-std=“ is good inspiration, but clearly the wrong specific name.
- The implementation should be straight forward: the flag should get plumbed
through to a field in swift::LangOptions. Code that diverges can then check it.
- Handling divergence in the standard library is another big issue. We have
some ideas here, but it depends on having the compiler work done anyway to hook
into.
> How many versions back would the compiler be expected to support? Should the
> Swift 5 compiler still support Swift 3 code?
To be determined. Swift 4 should definitely support Swift 3, but Swift 5
perhaps not. We can decide that when Swift 4 is winding down.
-Chris
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