Open Radar

 
Summary:
Currently the `Hashable` protocol inherits from `Equatable` and adds the `hashValue: Int` property. Because of inheriting from Equatable, the Hashable protocol can only be used as a generic constraint, which means it isn't possible to write a generic function when you only need the hashValue from a group of objects, rather than an equality check.

The protocols would need to be:

protocol _Hashable {
    var hashValue: Int { get }
}

protocol Hashable: _Hashable, Equatable { }

Steps to Reproduce:
1. Open Xcode
2. Create a new playground
3. Enter the following code:

func combinedHashValue(args: _Hashable...) -> Int {
    return args.reduce(0) { $0 + $1.hashValue }
}


Expected Results:
The code would compile and return the sum of the hashValues.