Implement #672

Source/SocketIOClient.swift

@@ -234,7 +234,11 @@ open class SocketIOClient : NSObject, SocketIOClientSpec, SocketEngineClient, So
     /// - parameter event: The event to send.
     /// - parameter items: The items to send with this event. May be left out.
     open func emit(_ event: String, _ items: SocketData...) {
-        emit(event, with: items)
+        do {
+            emit(event, with: try items.map({ try $0.socketRepresentation() }))
+        } catch {
+            fatalError("Error creating socketRepresentation for emit: \(event), \(items)")
+        }
     }
 
     /// Same as emit, but meant for Objective-C
@@ -267,7 +271,11 @@ open class SocketIOClient : NSObject, SocketIOClientSpec, SocketEngineClient, So
     /// - parameter items: The items to send with this event. May be left out.
     /// - returns: An `OnAckCallback`. You must call the `timingOut(after:)` method before the event will be sent.
     open func emitWithAck(_ event: String, _ items: SocketData...) -> OnAckCallback {
-        return emitWithAck(event, with: items)
+        do {
+            return emitWithAck(event, with: try items.map({ try $0.socketRepresentation() }))
+        } catch {
+            fatalError("Error creating socketRepresentation for emit: \(event), \(items)")
+        }
     }
 
     /// Same as emitWithAck, but for Objective-C

Source/SocketTypes.swift

@@ -25,7 +25,34 @@
 import Foundation
 
 /// A marking protocol that says a type can be represented in a socket.io packet.
-public protocol SocketData {}
+///
+/// Example:
+///
+/// ```swift
+/// struct CustomData : SocketData {
+///    let name: String
+///    let age: Int
+///
+///    func socketRepresentation() -> SocketData {
+///        return ["name": name, "age": age]
+///    }
+/// }
+///
+/// socket.emit("myEvent", CustomData(name: "Erik", age: 24))
+/// ```
+public protocol SocketData {
+    // MARK: Methods
+
+    /// A representation of self that can sent over socket.io.
+    func socketRepresentation() throws -> SocketData
+}
+
+public extension SocketData {
+    /// Default implementation. Only works for native Swift types and a few Foundation types.
+    func socketRepresentation() -> SocketData {
+        return self
+    }
+}
 
 extension Array : SocketData { }
 extension Bool : SocketData { }