swift @objc dynamic
@objc vs @objc dynamic
@objc: Objective-C entry points
One can explicitly write @objc
on any Swift declaration that can be expressed in Objective-C.
@objc dynamic:入口+动态派发机制。using the Objective-C message send mechanism。
dynamic
no longer infers @objc
A declaration that is dynamic
will no longer infer @objc
. For example:
This change is intended to separate current implementation limitations from future language evolution: the current implementation supports dynamic
by always using the Objective-C message send mechanism, allowing replacement of dynamic
implementations via the Objective-C runtime (e.g., class_addMethod
and class_replaceMethod
). In the future, it is plausible that the Swift language and runtime will evolve to support dynamic
without relying on the Objective-C runtime, and it's important that we leave the door open for that language evolution.
This change therefore does two things. First, it makes it clear that the dynamic
behavior is tied to the Objective-C runtime. Second, it means that well-formed Swift 4 code will continue to work in the same way should Swift gain the ability to provide dynamic
without relying on Objective-C: at that point, the method foo()
above will become well-formed, and the method bar()
will continue to work as it does today through the Objective-C runtime. Indeed, this change is the right way forward even if Swift never supports dynamic
in its own runtime, following the precedent of SE-0070, which required the Objective-C-only protocol feature "optional requirements" to be explicitly marked with @objc
.
https://github.com/apple/swift-evolution/blob/master/proposals/0160-objc-inference.md
备注:
@objc
exposes the variable to the ObjC runtime. dynamic
tells the runtime to use dynamic dispatch instead of the default static dispatch. dynamic
also implies @objc
so @objc dynamic
is redundant. You mostly utilize them in KVO and Cocoa Binding
https://stackoverflow.com/questions/48559768/what-does-objc-dynamic-var-mean-in-swift-4
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