I have seen a few articles or video's on iOS 15's new Self._printChanges() function, but can not find any documentation on it anywhere. Does anyone know where Apple documented this new function? It is pretty obvious how to use it, but I would like to see what more we can do with it and knowing more about it would be helpful. Even Xcode's lookup's yield nothing. Anyone find anything?

CodePudding user response：

Unfortunately, _printChanges() is a private API, which is why it's undocumented. The only reason so many videos and articles referenced it is because an Apple engineer mentioned it during WWDC21. Here's what they said:

It's not technically API-notice the leading underscore — so should only be used in debugging. My one sentence pro-tip is the extent of the docs I'm afraid.

However, Xcode does show a summary when you Option Click.

Summary
When called within an invocation of body of a view of this type, prints the names of the changed dynamic properties that caused the result of body to need to be refreshed. As well as the physical property names, “@self” is used to mark that the view value itself has changed, and “@identity” to mark that the identity of the view has changed (i.e. that the persistent data associated with the view has been recycled for a new instance of the same type).