[3.0] SE-0140: Bridge Optionals to nonnull ObjC objects by bridging their payload, or using a sentinel. #4891
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…ayload, or using a sentinel. id-as-Any lets you pass Optional to an ObjC API that takes `nonnull id`, and also lets you bridge containers of `Optional` to `NSArray` etc. When this occurs, we can unwrap the value and bridge it so that inhabited optionals still pass into ObjC in the expected way, but we need something to represent `none` other than the `nil` pointer. Cocoa provides `NSNull` as the canonical "null for containers" object, which is the least bad of many possible answers. If we happen to have the rare nested optional `T??`, there is no precedented analog for these in Cocoa, so just generate a unique sentinel object to preserve the `nil`-ness depth so we at least don't lose information round-tripping across the ObjC-Swift bridge. Making Optional conform to _ObjectiveCBridgeable is more or less enough to make this all work, though there are a few additional edge case things that need to be fixed up. We don't want to accept `AnyObject??` as an @objc-compatible type, so special-case Optional in `getForeignRepresentable`. Implements SR-0140 (rdar://problem/27905315).
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@swift-ci Please test |
jckarter
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id-as-Any lets you pass Optional to an ObjC API that takes
nonnull id, and also lets you bridge containers ofOptionaltoNSArrayetc. When this occurs, we can unwrap the value and bridge it so that inhabited optionals still pass into ObjC in the expected way, but we need something to representnoneother than thenilpointer. Cocoa providesNSNullas the canonical "null for containers" object, which is the least bad of many possible answers. If we happen to have the rare nested optionalT??, there is no precedented analog for these in Cocoa, so just generate a unique sentinel object to preserve thenil-ness depth so we at least don't lose information round-tripping across the ObjC-Swift bridge.Making Optional conform to _ObjectiveCBridgeable is more or less enough to make this all work, though there are a few additional edge case things that need to be fixed up. We don't want to accept
AnyObject??as an @objc-compatible type, so special-case Optional ingetForeignRepresentable.Implements SE-0140 (rdar://problem/27905315).