Request and response

Implement IActor<TRequest, TResponse> when callers need a result.

public sealed record LookupUser(Guid Id);
public sealed record UserView(Guid Id, string Name);

public sealed class UserActor : IActor<LookupUser, UserView>
{
    public Task<UserView?> Receive(LookupUser message)
    {
        UserView user = new(message.Id, "Ada");
        return Task.FromResult<UserView?>(user);
    }
}

IActorRef<UserActor, LookupUser, UserView> users =
    system.Spawn<UserActor, LookupUser, UserView>();

UserView? user = await users.Ask(
    new LookupUser(id),
    TimeSpan.FromSeconds(2));

When the timeout elapses, Ask throws AskTimeoutException. Overloads can also include an explicit sender reference.

Admission-aware asks

For a bounded inbox, TryAsk checks capacity before creating reply machinery:

if (users.TryAsk(new LookupUser(id), out Task<UserView?>? reply))
{
    UserView? result = await reply;
}
else
{
    // Not enqueued: back off, retry, or shed the request.
}

A false result means the message was never delivered, so retrying is safe. See Backpressure and admission.