This. I asked that already and they not understand me very well.

I see no reason for each app to have its own version of "deprecated lib".

Also we can keep the libswiftCore_4.1.dylib, libswiftCore_5.0.dylib,
libswiftCore_5.1.dylib etc on the SO too. The default target must be
libswiftCore.dylib, but if need to use a specific feature on
libswiftCore_4.1.dylib why not.

Em seg, 15 de jan de 2018 às 16:54, Jacob Williams via swift-evolution <> escreveu:

> Pardon my lack of knowledge in this area, but is there not also a 3rd
> option available?
> (C) Split libswiftCore.dylib into two dylibs, both at the OS level. The
> *Deprecated.dylib would only be included when the application binary was
> compiled using a special -using-deprecated flag that signifies this app
> needs at least one of the deprecated APIs? Then the code signing
> verification you mention wouldn’t be a part of the apps that use deprecated
> APIs.
> If this is not possible because all OS-level .dylibs MUST be included for
> whatever reason then just disregard me, as I’m not an expert on this area
> of Swift.
> On Jan 12, 2018, at 5:43 PM, Ted Kremenek via swift-evolution <
>> wrote:
> Hi Chris,
> Instead of responding to each of your point bit-by-bit, I’ll try a
> different tactic to explain my reasoning — which may be wrong — by
> explaining how I see things top down with the tradeoffs they incur.  I’m
> going to say a bunch of things I know *you* know, but others are on this
> thread and I’ll state things for end-to-end clarity.
> It seems to me that we are talking about two possible scenarios: (1) the
> status quo of keeping everything in libswiftCore.dylib or (2) splitting
> libswiftCore.dylib into two dylibs, one which includes some of the
> “deprecated” APIs.  I’ll enumerate what I think are the tradeoffs/benefits
> we will see with both scenarios, and see where the mismatch in our “talking
> past each other” is happening.
> In both cases (A) and (B), with ABI stability the Standard Library has the
> option to ship in the OS.  Thus applications using Swift on (say) iOS would
> no longer need to include libswiftCore.dylib in the app when running on an
> OS that shipped with the Standard Library.
> With that in mind, here are the tradeoffs as I see between scenarios (A)
> and (B):
> (A) Status quo: Keep shipping everything in libswiftCore.dylib
> - Applications running on an OS with the Standard Library would no longer
> have *any* of the currently libswift*.dylib’s embedded inside the
> application bundle because they would just use the one in the OS.
> - One benefit of using libswift*.dylibs in the OS as opposed to those
> embedded inside the app bundle is that there is a non-neglible startup time
> improvement, as the code signing verification that happens when an app
> launches would be faster as it would not need to verify each of these
> dylibs that were previously embedded in the app.  We should consider this
> the new baseline for app startup time for an app running on an OS with an
> ABI stable Standard Library.
> - We continue to support the deprecated APIs for some time, possibly
> indefinitely, even when better alternatives come around.
> (B) Split libswiftCore.dylib into two dylibs, one that gets embedded in
> the app bundle
> In the second scenario, we split out the deprecated APIs into a separate
> dylib, say libswiftCoreDeprecated.dylib.  That solution would have the
> following characteristics:
> - Like scenario (A), app bundles would not need to embed
> libswiftCore.dylib when running on an OS that had an ABI-stable Standard
> Library.
> - Compared to scenario (A), the OS shipping the Standard Library would
> have a slightly smaller libswiftCore.dylib that didn’t carry the bits for
> the deprecated APIs.  This would be a benefit in the code size for the OS,
> but not for the app itself.
> - Any app using a deprecated API we put into libswiftCoreDeprecated.dylib
> (e.g., Mirrors) would need to embed libswiftCoreDeprecated.dylib inside
> their app bundle.  Compared to the new baseline I mentioned in (A), such
> apps would have a launch time regression once they started using any API in
> the libSwiftCoreDeprecated.dylib because code signing would need to verify
> the dylib, just like it does today with the libswiftCore.dylib that is
> embedded in every application.  They would also be slightly larger because
> the app bundle has the burden of hosting libswiftCoreDeprecated.dylib,
> instead of compared to scenario (A) where the implementations of the
> deprecated APIs are hosted by the libswiftCore.dylib that ships in the OS.
> - Because of binary compatibility concerns, after Swift 5 we would *never*
> be able to “take out” any further APIs from libswiftCore.dylib and put them
> in libswiftCoreDeprecated.dylib.  This factorization can only happen once.
> - There is some slight additional complexity added to the compiler and
> build system to support this spit of the Standard Library into multiple
> dylibs.  It’s not a huge concern but it does exist and it is not free both
> in terms of implementing and maintaining.
> - We continue to support the deprecated APIs for some time, possibly
> indefinitely, even when better alternatives come around.  We *may* be able
> to completely sunset these APIs by having a future version of the Swift
> compiler simply refuse to build projects that use the deprecated (now
> obsoleted) APIs.  At that point, these apps need to move to using the newer
> API alternatives, or not upgrade to using a new Swift compiler.
> With these points in mind, both scenarios are (by construction) very
> similar.  Scenario (B) potentially provides a bit more flexibility in
> outright sunsetting deprecated APIs down the road — but only the APIs we
> deem today should be on that path. In the future when we decide to
> deprecate APIs in the Standard Library we will need to follow the same kind
> of deprecation-and-obsoletion path as other binary frameworks in macOS/iOS,
> which may mean keeping API implementations around for a very long time just
> for the purpose of binary compatibility.
> If you agree with me up to this point, to me this boils down to a tradeoff
> of some slightly increased opportunity to sunset some APIs in the future
> for a slight reduction in size of the Standard Library today (as it ships
> in the OS).  Most apps that don’t use these APIs won’t care either way,
> because even if we go with scenario B if they don’t use one of the
> deprecated APIs they will essentially be in scenario A (and thus get the
> benefit of using a Standard Library from the OS).  In scenario B, those
> apps that use the deprecated APIs will be slightly punished with slightly
> increased app bundle size and startup time.  Further, these APIs really
> can’t be deprecated right now (in terms of marking them deprecated in the
> module) until we have actual alternatives, so for the users that really
> want to use Mirrors today (which I agree may be small) that is the main
> tool they have to obtain that functionality.  Such users will pay a cost —
> albeit probably pretty minor — in scenario B.
> I have not done the measurements of the impact in code size to the
> Standard Library of removing Mirrors, but I hypothesize it is relatively
> modest (I will look at verifying this hypothesis).
> Do these observations align with what you are proposing, or am I missing a
> critical detail?
> Ted
> On Jan 11, 2018, at 11:56 AM, Chris Lattner <> wrote:
> On Jan 11, 2018, at 12:01 AM, Ted Kremenek <> wrote:
> The nice thing about this is that only people who use these things would
> have to pay the cost, and you can directly message this by deprecating all
> the stuff in it.  Think about it as an overlay for the Swift standard
> library :-)
> Hi Chris,
> Even if we split the APIs into two sets, with an “ABI unstable” subset, we
> are still going to “carry round these ’suboptimal APIs’” because clients
> are using them today and those APIs — without an active plan to remove them
> — *are* a part of the Standard Library.  We’ve past the point in Swift
> where we can just rip them out (you said so yourself in a follow up email).
> Who is “we” and how do you define carry?
> I think you’re saying that they will remain part of the swift project (in
> the “SwiftDeprecated” module) for effectively ever.  If so, I agree, and
> that’s the point.  The point is that the code can continue to exist and
> service the few people who need it (and will become even fewer over the
> years) without causing *harm* to the Swift ecosystem over the near or long
> term.  That’s the feature.
> It feels to me that the main advantage of the overlay is a solution to
> remove out pieces of the Standard Library that will be used in practice
> less, and thus clients don’t “pay the cost” when they don’t use them.
> Yes, exactly.
> But I think we should be honest about what that “cost” actually is, as
> these APIs aren’t going away right now.  These suboptimal APIs will stay
> around at least until better ones are created, and even then some existing
> clients will want to rely on the existing suboptimal APIs anyway even if
> others want to take advantage of newer, better APIs and idioms.
> I’m not sure what you mean.  I’m talking about two things specifically:
> 1) APIs that are already deprecated and have replacements.  The deprecated
> version goes in this library, avoid carrying them around forever.
> 2) APIs that are used by extremely narrow audiences, which were added
> without much consideration and that have not been redesigned since Swift
> 1.  Mirror’s are an example of this.  I’m arguing that these should be
> moved to this SwiftDeprecated module - but not actually deprecated until a
> replacement exists.
> I don’t see how this is bad for anyone, and I think this provides a
> significant process improvement compared to your current approach, which
> forces you to lock down APIs now without careful consideration just because
> they are not “important enough”.
> The main cost I see here that we save by having an “overlay for the
> Standard library" is code size.
> I don’t understand this point.
> On macOS/iOS it is true that applications embed a copy of the Standard
> Library within them and thus pay a real cost in the Standard Library’s
> actually payload size in their own app.  However, the only reason that is
> necessary today is because we don’t have ABI stability.  With ABI
> stability, other options for shipping the Standard Library — such as
> shipping it in the OS — become possible, and thus the burden of shouldering
> that “cost” of code size shifts around.  Then the tradeoffs of having an
> overlay for the Standard Library are different.  In a world with ABI
> stability, is it better to have a Standard Library "overlay" that only some
> clients use, and embed within their application bundle, than just eat that
> cost in the Standard Library to be shared by potentially multiple clients
> installed on a system?  I think it really comes down to the numbers.  In
> that case, are we really just talking about Mirrors?  I haven’t run the
> numbers here, but my intuition tells me we are talking about a relatively
> small code size impact overall.
> This comment doesn’t make a lot of sense to me, perhaps we’re talking
> across each other.  The point of the design that I’m advocating for is that
> all apps (that deploy to iOS-next or later) get a immediate improvement
> from abi stability: the vast majority of the standard library is not put
> into their app bundle.  Further, the vastly most common apps - those that
> are not using mirrors or deprecated APIs, also do not include the
> SwiftDeprecated module.
> Only the tiny minority of apps that do use these APIs would have a copy of
> SwiftDeprecated in their app dylib, but they have a path to fix that, and
> they would still see a huge improvement from the bulk of the standard
> library being out of their app bundle.
> There’s also other potential performance implications from doing this
> split.
> This doesn’t make sense to me.  We’re not talking about taking comonly
> used apis here.  Mirrors are not performance sensitive at all, and neither
> are deprecated wrappers of renamed APIs.
> Being able to have the Standard Library be in the OS has potential major
> implications on the startup time of Swift applications.
> It is great for app developers to have an incentive to stop using
> deprecated APIs! :-)
> Can you elaborate a bit more on the specific “cost” factors you are using
> when proposing to have a Standard Library overlay?
> I think it is possible that you’re reading too much into the “overlay"
> word here, so ignore that.  The design I’m proposing is really simple:
> 1. The vast majority of the standard library goes into the OS.  This
> includes all the string, array, and other stuff people use.
> 2. The deprecated wrappers and obscure APIs go into a new module, and that
> module doesn’t go into the OS.  Only people that use it pay to cost.
> This isn’t particularly complicated, if give you new ways to manage the
> process of stdlib ABI stability, and I don’t see the downside.
> -Chris
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