> On Apr 4, 2016, at 4:48 PM, Drew Crawford via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> Suppose *Apple* ships a framework that is only supported in iOS 9.3. As a
> direct consequence, the framework is only #available in iOS 9.3 or later.
>
> Suppose Jane links this framework into her iOS application. The deployment
> target for her application *can be any value*. She sets the framework to be
> weakly linked, and as long as the code that uses the Apple framework is
> guarded by a 9.3 availability check, she can deploy back to 8.0, 7.0, etc.
>
> Suppose *I* ship a custom framework that I only want to bother supporting for
> iOS 9.3 users. I'm not testing on old OS, I don't have CI on old OS, and
> quite frankly I have no idea if it works. And I'm not in the habit of
> shipping code that wasn't even tested on my machine. As a direct
> consequence, I set my framework deployment target to 9.3.
>
> Now Jane links this framework into her "deployment target 8.0" application.
> She weakly links it and uses availability checks just like she did with the
> Apple framework. But this time the compiler says no:
>
> error: module file's minimum deployment target is ios9.3 v9.3
>
> Jane now has a set of bad choices:
>
> 1. She can not use my framework at all
> 2. She can drop support for <9.3 entirely from her application in order to
> use my framework
> 3. She can convince me to support iOS 8, when I don't want to invest in the
> QA and test time.
> 4. She can convince me to set my deployment target to 8, try to find all my
> public APIs, sprinkle `@available(iOS 9.3, *)` everywhere and hope I didn't
> miss any. Spoiler alert: that's what I did all afternoon.
>
> This is too hard. IMO Jane should be able to use my "9.3+" frameworks as
> easily as she can use Apple's.
>
> IMO, when Jane imports a "DT 9.3" framework, into her "DT 8.0" application,
> it should A) import successfully, B) link weakly, and C) have
> `@availability(9.3, *)` overlayed on the interface.
I would not want this to be implicit behavior: it should be recorded in the
source with, e.g.,
@availability(iOS: 9.3) import YourCustomFramework
so that it is clear that the imported declarations are only available on iOS
9.3 or newer.
- Doug
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