C#•2y ago

❔ Generics

Hi, I commented the code to explain my issue

    public async Task DispatchAsync(IEventContext context)
    {
        var @event = _dictionary.Resolve<IEvent<TAggregateIdentifier>, TAggregateIdentifier>(context.Identifier, context.Payload);

        // 1. So far
        //  @event.GetType() -> MyEvent

        await _domain.HandleDomainAsync(@event);
    }

    public async Task HandleDomainAsync<TEvent>(TEvent @event) where TEvent : IEvent<TAggregateIdentifier>
    {
        // 2. So far
        // typeof(TEvent) -> IEvent<TAggregateIdentifier>
        // @event.GetType() -> MyEvent

        // 3. I have to use MakeGenericType to retrieve a list of IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, MyEvent>
        // as i cannot use TEvent directly.

        var type = typeof(IDomainEventHandler<,,>).MakeGenericType(typeof(TAggregateRoot), typeof(TAggregateIdentifier),
            @event.GetType());
        
        var service = _services.GetService(type);
        
        // 4. As GetService returned an object, I have to cast to IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent>
        // so i can call service.HandleAsync(@event)

        // 5. This doesn't work tho, as typeof(TEvent) -> IEvent<TAggregateIdentifier>, witch makes sence
        if(service is IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent> handler)
            await handler.HandleAsync(@event);

        // Question: I there any way I can make it working without using reflection to invoke HandleAsync ?
        // 
    }

    public async Task DispatchAsync(IEventContext context)
    {
        var @event = _dictionary.Resolve<IEvent<TAggregateIdentifier>, TAggregateIdentifier>(context.Identifier, context.Payload);

        // 1. So far
        //  @event.GetType() -> MyEvent

        await _domain.HandleDomainAsync(@event);
    }

    public async Task HandleDomainAsync<TEvent>(TEvent @event) where TEvent : IEvent<TAggregateIdentifier>
    {
        // 2. So far
        // typeof(TEvent) -> IEvent<TAggregateIdentifier>
        // @event.GetType() -> MyEvent

        // 3. I have to use MakeGenericType to retrieve a list of IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, MyEvent>
        // as i cannot use TEvent directly.

        var type = typeof(IDomainEventHandler<,,>).MakeGenericType(typeof(TAggregateRoot), typeof(TAggregateIdentifier),
            @event.GetType());
        
        var service = _services.GetService(type);
        
        // 4. As GetService returned an object, I have to cast to IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent>
        // so i can call service.HandleAsync(@event)

        // 5. This doesn't work tho, as typeof(TEvent) -> IEvent<TAggregateIdentifier>, witch makes sence
        if(service is IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent> handler)
            await handler.HandleAsync(@event);

        // Question: I there any way I can make it working without using reflection to invoke HandleAsync ?
        // 
    }

4 Replies

phaseshift•2y ago

// as i cannot use TEvent directly.

why? Regardless, it seems you want to be calling a generic method from a non-generic base class. There is a pattern that can do this for you with a bit of casting.

interface IBase
{
  void foo(object o);
}

abstract class Base<T> : IBase
{
  void foo(T t) {...};

  void food(object o) => foo((T)o);
}

interface IBase
{
  void foo(object o);
}

abstract class Base<T> : IBase
{
  void foo(T t) {...};

  void food(object o) => foo((T)o);
}

It's a bit ugly, but it lets you pass IBase around and call foo with a T as long as you know its right

xoneryOP•2y ago

Thanks for taking the time to read my post

// So far, I cannot use TEvent for the cast as
IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent>
// Is resolved as
IDomainEventHandler<MyAggregateRoot, MyAggregateIdentifier, IEvent<MyAggregateIdentifier>>
// And not
IDomainEventHandler<MyAggregateRoot, MyAggregateIdentifier, MyEvent>
// As I expected it to be, so the cast fails

// So far, I cannot use TEvent for the cast as
IDomainEventHandler<TAggregateRoot, TAggregateIdentifier, TEvent>
// Is resolved as
IDomainEventHandler<MyAggregateRoot, MyAggregateIdentifier, IEvent<MyAggregateIdentifier>>
// And not
IDomainEventHandler<MyAggregateRoot, MyAggregateIdentifier, MyEvent>
// As I expected it to be, so the cast fails

The pattern you showed works as expected but yea looks kinda ugly as i will need a Base class to wrap the casting... I would LOVE TEvent to be Resolved as MyEvent and not IEvent<MyAggregateIdentity>

if(service is IEventHandler handler)
    await handler.HandleAsync(@event);

if(service is IEventHandler handler)
    await handler.HandleAsync(@event);

phaseshift•2y ago

Yup. or switch to cpp and wait for 'deducing this' 😅

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Generics