I have a struct in Swift that looks like this:
internal struct MapKey {
internal let id: String
internal let values: [String:String]
}
extension MapKey: Equatable {}
func ==(lhs: MapKey, rhs: MapKey) -> Bool {
return lhs.id == rhs.id && lhs.values == rhs.values
}
I now have the need to use MapKey as the key in a Swift dictionary, which requires MapKey to conform to the Hashable protocol.
What would a correct implementation of Hashable be for a struct like this one?
extension MapKey: Hashable {
var hashValue: Int {
return ??? // values does not have a hash function/property.
}
}
I've been doing some research but failed to identify what the proper way to hash a dictionary is, as I need to be able to generate a hash value for values property itself. Any help is much appreciated.
I think you need to review your data model if you have to use a whole struct as a dictionary key. Anyhow, here's one way to do it:
internal struct MapKey: Hashable {
internal let id: String
internal let values: [String:String]
var hashValue: Int {
get {
var hashString = self.id + ";"
for key in values.keys.sort() {
hashString += key + ";" + values[key]!
}
return hashString.hashValue
}
}
}
func ==(lhs: MapKey, rhs: MapKey) -> Bool {
return lhs.id == rhs.id && lhs.values == rhs.values
}
This assumes that you don't have semicolon (;
) in id
or in the keys and values of values
. Hasable
implies Equatable
so you don't need to declare it conforming to Equatable
again.
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