Data Transfer and Types

When a method is called on a Worker, arguments are passed from the Main Thread to the Worker Thread, and results are passed back. Unlike standard function calls, this involves crossing thread boundaries.

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How Data Moves

Native (Isolates)

The Dart VM uses SendPort.send().

• Most objects are copied (deep cloned).
• Some objects (like String or TransferableTypedData) are transferred efficiently.
• The type system is preserved. A DateTime arrives as a DateTime.

Web (Web Workers)

The Browser uses worker.postMessage().

• Data is serialized using the Structured Clone Algorithm.
• Type Erasure: Dart objects effectively lose their class identity.
  • List<int> might arrive as a generic Array.
  • Map<String, int> might arrive as a generic Object or Map.
  • Custom classes (e.g. Person) cannot be sent directly without marshaling.

Supported Types (Out of the Box)

• Null (null)
• Booleans (bool)
• Numbers (int, double - see Converters for Web caveats)
• Strings (String)
• Collections (List, Map, Set) of the above.
• Uint8List and other TypedData.
• SendPort (Native only, for direct isolate comms).

Custom Types

To send a custom class (e.g., User, Product), you must use a Marshaler.

Next Step: Learn more about Marshaling.