Open Radar

 
Summary:
The documentation for NSMergeByPropertyStoreTrumpMergePolicyType and NSMergeByPropertyObjectTrumpMergePolicyType is the wrong way around. The header file descriptions are the correct way around.

Using ‘external’ is a bit confusing without saying external to what. It seems you mean external to the current process: in other words, in the persistent store.

Steps to Reproduce:
Read the descriptions on https://developer.apple.com/documentation/coredata/nsmergepolicytype?language=objc

Expected Results:
NSMergeByPropertyStoreTrumpMergePolicyType
A policy that merges conflicts between the persistent store's version of the object and the current in-memory version by individual property, with the persistent store’s changes trumping in-memory changes.

NSMergeByPropertyObjectTrumpMergePolicyType
A policy that merges conflicts between the persistent store's version of the object and the current in-memory version by individual property, with the in-memory changes trumping persistent store's changes.


Actual Results:
NSMergeByPropertyStoreTrumpMergePolicyType
A policy that merges conflicts between the persistent store's version of the object and the current in-memory version by individual property, with the in-memory changes trumping external changes.

NSMergeByPropertyObjectTrumpMergePolicyType
A policy that merges conflicts between the persistent store's version of the object and the current in-memory version by individual property, with the external changes trumping in-memory changes.

Version:
Today

Notes:
Header file, NSMergePolicy.h, is correct and says:

// This singleton policy merges conflicts between the persistent store's version of the object and the current in memory version. The merge occurs by individual property. For properties which have been changed in both the external source and in memory, the external changes trump the in memory ones.
COREDATA_EXTERN id NSMergeByPropertyStoreTrumpMergePolicy API_AVAILABLE(macosx(10.4),ios(3.0));    

// This singleton policy merges conflicts between the persistent store's version of the object and the current in memory version. The merge occurs by individual property. For properties which have been changed in both the external source and in memory, the in memory changes trump the external ones.
COREDATA_EXTERN id NSMergeByPropertyObjectTrumpMergePolicy API_AVAILABLE(macosx(10.4),ios(3.0));