Change type constraint of pipeline behavior to allow easier chaining

[darjanbogdan]

We have encountered an interesting "problem" related to the newly introduced PipelineBehavior type constraint in the latest version of the library.

To elaborate a bit, we had a few flag interfaces that were meant to enable certain pipeline behavior based on its type constraints. For example, ITransactionalRequest or IScopedRequest. Such interfaces inherited IBaseRequest since response types are not important for the behaviors that use them as type constraints:

public class TransactionalPipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
        where TRequest : ITransactionalRequest
{
// implementation
}

Such composition made it possible to use ITransactionalRequest for any type of request (ie IRequest, IRequest<TResponse>), and behavior would be "enabled" no matter whether a request returns Unit or TResponse

However due to the subtle change in the type constraint IPipelineBehavior<TRequest, TResponse> where TRequest : IRequest<TResponse> it forces library consumers to create pairs of interfaces without real need in my opinion. The above example doesn't work anymore since ITransactionalRequest doesn't inherit from IRequest<TResponse> so the type can't be inferred. That leaves us with the following fix:

interface ITransactionalRequest<TResponse> : IRequest<TResponse> { }
interface ITransactionalRequest : ITransactionalRequest<Unit> { }

The fix itself is not a big deal, but I think if we change the type constraint as proposed in the PR, we would be able to keep the benefits of knowing that pipeline behavior works with known request objects, and we wouldn't force more complex, or generic flag interfaces elsewhere in 3rd party code. After all, that is the intended purpose of IBaseRequest interface.

I'm curious to hear your opinion, thank you!

PS. I know I haven't asked whether this change is wanted or not, but I wished to cut some corners, hence the PR.

[jbogard]

Yeah I'm not sure the generic constraints really added much except work.

[jbogard]

Sorrryyyyy everyone 😬