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Runtime-Typed Dispatch (Send(object))

For message bus, command queue, and event sourcing scenarios where the consumer deserializes a request from the wire and only has an object reference at runtime:

// Producer — serialize command + type
var command = new CreateUser("[email protected]");
queue.Push((JsonSerializer.Serialize(command), command.GetType().AssemblyQualifiedName));

// Consumer — deserialize and dispatch without knowing TResponse
(string raw, string typeName) = queue.Pop();
var type = Type.GetType(typeName)!;
var command = JsonSerializer.Deserialize(raw, type)!;

var result = await mediator.Send(command); // runtime-typed dispatch → ValueTask<object?>

The Send(object) overload uses a compile-time generated FrozenDictionary<Type, DispatchDelegate> dispatch table — same architecture as Publish(object). No reflection, no MakeGenericType, fully AOT-safe.

How It Works

• The source generator registers a dispatch delegate for every request type discovered at compile time
• At runtime, Send(object) looks up the delegate by request.GetType() (O(1) frozen dictionary lookup)
• The delegate casts the object to the concrete request type, resolves the handler/pipeline, and returns the response boxed as object?
• TResponse boxing only occurs on this path — the standard Send<TRequest, TResponse>() path remains zero-allocation

Overload Resolution

Send(object) is implemented as an extension method (not an interface method). This ensures the generated typed extension methods are always preferred when the compile-time type is known:

// Typed extension wins — zero-overhead, no boxing
var result = await mediator.Send(new Ping()); // → ValueTask<int>

// Object extension — runtime dispatch, response boxed
object request = new Ping();
var result = await mediator.Send(request);   // → ValueTask<object?>

Performance

Path	Lookup	Boxing	Use case
Send(new Ping())	Static generic (~7 ns)	None	Normal application code
Send((object)ping)	FrozenDictionary (~2-5 ns)	TResponse → object?	Queue/bus consumers

The FrozenDictionary lookup + boxing cost is negligible compared to the deserialization cost (~μs) in queue/bus scenarios.