Allow async Task<IRuleContext> rules

[rockfordlhotka]

Consider enhancing the rules engine to allow Execute methods that return Task<RuleContext>.

Right now async rules are void or async void, but it would be acceptable to have an overload of Execute that would be async Task<RuleContext>.

In such a scenario having the rule call context.Complete() would result in an exception, because completion of the rule would be indicated by return context instead.

I don't think there'd be any other changes to the way rules are implemented - so this is basically a cosmetic change to the way rules are implemented to help avoid having people implement async void methods (which are normally a bad thing).

[JasonBock]

I'd name the new method "ExecuteAsync" to follow standard .NET patterns and to differentiate it from the old-school "Execute" way.

[rockfordlhotka]

The rule engine is interface-based, so adding a new method name would expand the interface - thus leaving the question of whether the engine should call Execute or ExecuteAsync given that both would have to be "implemented" by the rule.

[JasonBock]

Hmmm...is there a way this could be done so you have a AsyncBusinessRule class, and that's what's used for "new" async rules?

[rockfordlhotka]

Thinking about this more today. The rule engine is interface-based. So I suppose the answer is three interfaces.

  public interface IBusinessRuleBase {}

  public interface IBusinessRule : IBusinessRuleBase
  {
    void Execute(IRuleContext context);
  }

  public interface IBusinessRuleAsyncBase : IBusinessRuleBase
  {
    Task Execute(IRuleContext context);
  }

Also add a new BusinessRuleAsync base class that implements the new interface.

Rules would then look like this (sync, async-old, async-new):

  public class MyRule : BusinessRule
  {
    public override void Execute(IRuleContext context)
    {
      // sync rule goes here
    }
  }

  public class MyRule : BusinessRule
  {
    public MyRule() { IsAsync = true; }

    public override async void Execute(IRuleContext context)
    {
      // async rule goes here
      context.Complete();
    }
  }

  public class MyRule : BusinessRuleAsync
  {
    public override async Task Execute(IRuleContext context)
    {
      // async rule goes here
    }
  }

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