Original StackOverflow post:
https://stackoverflow.com/questions/46924554/redundant-superclass-constraint-in-swift-4
I'm getting a Redundant superclass constraint... warning in swift4: (paste in a
playground)
import CoreData
class Item : NSManagedObject {}
protocol DataSourceProtocol {
associatedtype DataSourceItem : NSManagedObject
}
protocol DataSourceProtocolProvider : class { }
extension DataSourceProtocolProvider {
func createDataSource<T: DataSourceProtocol>(dataSource: T)
where T.DataSourceItem == Item {
}
}
On the createDataSource<T: DataSourceProtocol> declaration I get the following
warning:
Redundant superclass constraint 'T.DataSourceItem' : 'NSManagedObject'
I thought that you could specify that an associatedtype could be used with the
== operator to constrain the associatedtype to a specific type. I want to have
a func createDataSource<T: DataSourceProtocol>(dataSource:T) where the
DataSourceItem is an Item.
If I replace the == operator with : then the warning goes away:
extension DataSourceProtocolProvider {
func createDataSource<T: DataSourceProtocol>(dataSource: T)
where T.DataSourceItem : Item {
}
}
This happens to be a completely different context now. This constraint
specifies that I want to have a func createDataSource<T:
DataSourceProtocol>(dataSource:T) where the DataSourceItem is a subclass of
Item. Which isn't the same thing as DataSourceItem is an Item object. Also, the
code runs fine with == so am I just not understanding how constraints work?
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