Decoding a nullable heterogeneous dictionary - swift

Question

I need to decode a dictionary of the form [(Heterogeneous object): CGFloat]?. I've got working extensions on the KeyedDecodingContainer that allow me to decode lists of and single heterogeneous objects however I'm struggling to convert these to work with a dictionary. Here is the working method for a optional array:
func decodeArrayIfPresent<T : Decodable, U : ClassFamily>(family: U.Type, forKey key: K) throws -> [T]? {
do {
var container = try self.nestedUnkeyedContainer(forKey: key)
var list = [T]()
var tmpContainer = container
while !container.isAtEnd {
let typeContainer = try container.nestedContainer(keyedBy: Discriminator.self)
let family: U? = try typeContainer.decodeIfPresent(U.self, forKey: U.discriminator)
if let type = family?.getType() as? T.Type {
list.append(try tmpContainer.decode(type))
}
}
return list
} catch DecodingError.keyNotFound {
return nil
} catch DecodingError.valueNotFound {
return nil
}
}
And this is where I've got to for a dictionary:
func decodeDictIfPresent<T : Decodable, U : ClassFamily>(family: U.Type, forKey key: K) throws -> [T: Any]? {
do {
var container = try self.nestedUnkeyedContainer(forKey: key)
var dict = [T: Any]()
var tmpContainer = container
while !container.isAtEnd {
let typeContainer = try container.nestedContainer(keyedBy: Discriminator.self)
let family: U? = try typeContainer.decodeIfPresent(U.self, forKey: U.discriminator)
if let type = family?.getType() as? T.Type {
list.append(try tmpContainer.decode(type))
}
}
return dict
} catch DecodingError.keyNotFound {
return nil
} catch DecodingError.valueNotFound {
return nil
}
}
Requirements:
protocol ClassFamily: Decodable {
/// The discriminator key.
static var discriminator: Discriminator { get }
/// Returns the class type of the object coresponding to the value.
func getType() -> AnyObject.Type
}
/// Discriminator key enum used to retrieve discriminator fields in JSON payloads.
enum Discriminator: String, CodingKey {
case type = "type"
}
Any pointers in the right direction would be appreciated! Thanks in advance