Move Enum and _NameMap.Name to the Swift 4.2 Hashable approach.

Author: thomasvl

Sources/SwiftProtobuf/Enum.swift

@@ -39,9 +39,15 @@ public protocol Enum: RawRepresentable, Hashable {
 }
 
 extension Enum {
+#if swift(>=4.2)
+  public func hash(into hasher: inout Hasher) {
+    hasher.combine(rawValue)
+  }
+#else  // swift(>=4.2)
   public var hashValue: Int {
     return rawValue
   }
+#endif  // swift(>=4.2)
 
   /// Internal convenience property representing the name of the enum value (or
   /// `nil` if it is an `UNRECOGNIZED` value or doesn't provide names).

Sources/SwiftProtobuf/NameMap.swift

@@ -68,9 +68,11 @@ fileprivate class InternPool {
   }
 }
 
+#if !swift(>=4.2)
 // Constants for FNV hash http://tools.ietf.org/html/draft-eastlake-fnv-03
 private let i_2166136261 = Int(bitPattern: 2166136261)
 private let i_16777619 = Int(16777619)
+#endif
 
 /// An immutable bidirectional mapping between field/enum-case names
 /// and numbers, used to record field names for text-based
@@ -127,13 +129,21 @@ public struct _NameMap: ExpressibleByDictionaryLiteral {
       }
     }
 
+  #if swift(>=4.2)
+    public func hash(into hasher: inout Hasher) {
+      for byte in utf8Buffer {
+        hasher.combine(byte)
+      }
+    }
+  #else  // swift(>=4.2)
     public var hashValue: Int {
       var h = i_2166136261
       for byte in utf8Buffer {
         h = (h ^ Int(byte)) &* i_16777619
       }
       return h
     }
+  #endif  // swift(>=4.2)
 
     public static func ==(lhs: Name, rhs: Name) -> Bool {
       if lhs.utf8Buffer.count != rhs.utf8Buffer.count {