some methods have discardableresults

Source/SocketIOClient.swift

@@ -347,6 +347,7 @@ public final class SocketIOClient : NSObject, SocketEngineClient, SocketParsable
 
     /// Adds a handler for an event.
     /// Returns: A unique id for the handler
+    @discardableResult
     public func on(_ event: String, callback: NormalCallback) -> NSUUID {
         DefaultSocketLogger.Logger.log("Adding handler for event: %@", type: logType, args: event)
 
@@ -358,6 +359,7 @@ public final class SocketIOClient : NSObject, SocketEngineClient, SocketParsable
 
     /// Adds a single-use handler for an event.
     /// Returns: A unique id for the handler
+    @discardableResult
     public func once(event: String, callback: NormalCallback) -> NSUUID {
         DefaultSocketLogger.Logger.log("Adding once handler for event: %@", type: logType, args: event)
 

Source/SocketStringReader.swift

@@ -38,6 +38,7 @@ struct SocketStringReader {
         currentIndex = message.startIndex
     }
     
+    @discardableResult
     mutating func advance(by: Int) -> String.Index {
         currentIndex = message.characters.index(currentIndex, offsetBy: by)