Conforming to Hashable protocol?

Question

I'm trying to make a dictionary with the key as a struct I've created and the value as an array of Ints. However, I keep getting the error:

Type 'DateStruct' does not conform to protocol 'Hashable'

I'm pretty sure I've implemented the necessary methods but for some reason it still doesn't work.

Here's my struct with the implemented protocols:

struct DateStruct {     var year: Int     var month: Int     var day: Int      var hashValue: Int {         return (year+month+day).hashValue     }      static func == (lhs: DateStruct, rhs: DateStruct) -> Bool {         return lhs.hashValue == rhs.hashValue     }      static func < (lhs: DateStruct, rhs: DateStruct) -> Bool {         if (lhs.year < rhs.year) {             return true         } else if (lhs.year > rhs.year) {             return false         } else {             if (lhs.month < rhs.month) {                 return true             } else if (lhs.month > rhs.month) {                 return false             } else {                 if (lhs.day < rhs.day) {                     return true                 } else {                     return false                 }             }         }     } } 

Can anybody please explain to me why I'm still getting the error?

Answer 1

You're missing the declaration:

struct DateStruct: Hashable { 

And your == function is wrong. You should compare the three properties.

static func == (lhs: DateStruct, rhs: DateStruct) -> Bool {     return lhs.year == rhs.year && lhs.month == rhs.month && lhs.day == rhs.day } 

It's possible for two different values to have the same hash value.

Answer 2

Btw

var hashValue: Int  

is obsolete (except in the legacy NSObject inheritance trees).

    func hash(into hasher: inout Hasher)     {         hasher.combine(year);         hasher.combine(month)      ... 

is the new way