Removing NSNull from Key Path Results with Partial Matches

Question

Created Feb ’16

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Participants 2

Given a data structure with mismatching objects:

1> import Foundation
2> let d: NSDictionary = ["test": [["name": "Dick", "age": 101], ["name": "Jane"]]]

valueForKeyPath:

will return the values for the total number of sub-objects:

3> d.valueForKeyPath("test.name") as! NSArray
$R2: NSArray = "2 values" {
  [0] = "Dick"
  [1] = "Jane"
}

Even when the leaf key doesn't exist in all cases:

4> d.valueForKeyPath("test.age") as! NSArray
$R3: NSArray = "2 values" {
  [0] = Int64(101)
  [1] = {
    NSObject = {
      isa = NSNull
    }
  }
}

Is there some way to only get the existing

age

s, without an instances of

NSNull

?

@distinctUnionOfArrays

and so on helps if there are multiple sub-objects without the leaf key, but you're still left with the one

NSNull

.

On a somewhat side note, if the leaf key is entirely unknown, then only

NSNull

s are returned:

5> d.valueForKeyPath("test.dog") as! NSArray
$R4: NSArray = "2 values" {
  [0] = {
    NSObject = {
      isa = NSNull
    }
  }
  [1] = {
    NSObject = {
      isa = NSNull
    }
  }
}

In contrast, if the root key is unknown,

nil

is returned:

6> d.valueForKeyPath("dog.name")
$R5: AnyObject? = nil

This logic strikes me as inconsistent, but perhaps I'm missing something?

(This is cross-posted from Stack Overflow.)

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Answer 1

QuinceyMorris OP

Feb ’16

The first thing you tried is a (fairly) obscure feature of KVC, where objects in a collection can be examined to see whether they respond to given method. The second thing is a (fairly) clunky feature of KVC that tries to provide some pseudo-scripting for bindings.

If you're doing this in code, use the NSDictionary method 'keysOfEntriesPassingTest' or 'keysOfEntriesWithOptions:passingTest'.

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