Vendor-Extensions.md

@@ -124,3 +124,15 @@ definitions:
 #### x-protobuf-index
 
 For assigning field numbers: https://developers.google.com/protocol-buffers/docs/proto3#assigning_field_numbers
+
+### Swift
+#### x-swift-hastable
+
+To extends the model with `Hashable`, e.g. 
+```
+public struct Pet: Codable {
+```
+becomes 
+```
+public struct Pet: Codable, Hashable {
+```
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