Torben Hagensen, @[email protected]

Principal Architect at Systematic

[Vaughn Vernon @VaughnVernon]

I advocate avoiding the use of the Separated Interface pattern unless an interface is actually useful. I covered this in "Implementing Domain-Driven Design" in the "Domain Services" chapter. At the time and still today, frameworks such as Spring advocated using interfaces right next to the single implementing class. In Java, this was the typucal outcome:

ProposalService
ProposalServiceImpl

When scanning code, I learned filter in pairs. It's annoying because if you have a single implementation, (a) you have to maintain two sources, (b) the interface buys you nothing, (c) it's noisy, and (d) it's ugly.

So .NET developers will say that doesn’t happen to them because:

IProposalService
ProposalService

Yay! What? Less ugly, still all the other stuff. Besides, do you really say "I proposal service" to business collaborators? I refuse to, and I hope you don't. So now the noise is on the interface. Great.

Okay, if your blood isn't boiling by this point, you're probably wondering when Separated Interface is useful. Look no further than the pattern definition, a la P of EAA:

"Defines an interface in a separate package [namespace] from its implementation."

And:

"You can improve the quality of its design by reducing the coupling between the system's parts. A good way to do this is to group the classes into packages and control the dependencies between https://t.co/lb69KSSedx can then follow rules about how classes in one package can call classes in another - for example, one that says that classes in the domain layer may not call classes in the presentation package." [PofEAA] (reference below)

The two package/namespace (DDD Module) situations are:

1. Different implementations
2. Separation of concerns with loose coupling

I list "different implementations" first because that's the typical argument *against* Separated Interface. Huh? Yeah, "you'll almost never have more than one implementation." Sure, but this misses the whole reason behind point 2.

A chief architectural concern is loose/weak coupling, including not coupling business concerns with technical concerns. And there's another such concern: *direction of dependencies*.

Whether you are using Ports and Adapters or Layers, direction of dependencies matters. And if you are using Layers, the only way to keep yourself out of a bind with direction is to move the Infrastructure layer to the top. This is embodied in the Dependency Inversion Principle.

Bingo. You've got to declare an interface in a lower-level layer and put it's *even* single implementation in the Infrastructure. And that's the mentality that the beautiful and beautifully simplistic Ports and Adapters buys you. It's guides a way of thinking, not just a structure.

So, you want to be an architect? Then design like one. Hackers will hack.

P.S. I think this is my first blog post in what used to be a micro blogging app. I think I'll capture this in a blog post with pictures and all.

[PofEAA] https://t.co/tzKNIYGyDU

[Torben Hagensen, @[email protected] @TMHagensen]

@TotherAlistair What about the context? I guess both try to set the context of what to solve.

[Allen Holub. https://linkedIn.com/in/allenholub @allenholub]

Yet again, @Gartner_inc gets it entirely wrong (they really need to hire me 😄). I've fixed their diagram with a few minor mods:

[Torben Hagensen, @[email protected] @TMHagensen]

Check out my latest article: Handling Requirements in Agile Product Development https://t.co/FpRvRYLR25

[Shreyas Doshi @shreyas]

A thread of product management frameworks:

(this might be useful if you are a product manager, product leader, or founder)

[Torben Hagensen, @[email protected] @TMHagensen]

@bethcodes I usually talk about why development of new features tend to take longer (cost more) as a system gets larger and older, which we IMO can reduce by continuously keeping the code base sound.
Even finance folks seem to understand that. We developers must remind them, though 😉

[Torben Hagensen, @[email protected] @TMHagensen]

Yay, I am not the only one to say that pull request reviews are of little value and slows everything down.

Thanks, @jessitron, for this insightful article.

[Jessica Kerr @jessitron]

What if we treated our team like a distributed system and required a quorum for writes?
It might solve the problem of slow pull request reviews.
https://t.co/mdTWOrvaLt

[Torben Hagensen, @[email protected] @TMHagensen]

I wish more sites would take this approach.
https://t.co/T5Bgdcmkdc

[Torben Hagensen, @[email protected] @TMHagensen]

My former collegue Jan Reher shares valuable insight in this blog post. It's really worth the 10 minutes read.
https://t.co/2ViqN3ybei

[The Other Alistair @TotherAlistair]

Looks so true to me (thx John Miller)

[Torben Hagensen, @[email protected] @TMHagensen]

Interesting approach to a somewhat scaled agile that actually seems quite agile 👍
https://t.co/YP9z3NsjxA

[Marty Cagan @cagan]

The articles on empowered product teams continue to inspire some great conversations that have helped me to uncover additional areas of product confusion. I just published a new article on a fundamental but often misunderstood topic: https://t.co/59NSuDpO2z

[Torben Hagensen, @[email protected] @TMHagensen]

Excellent illustration 👍

[Greg Young @gregyoung]

Eventual Consistency

[Torben Hagensen, @[email protected] @TMHagensen]

@VaughnVernon @TotherAlistair and his Heart of Agile boils Agile down to the 4 Words: Collaborate, Reflect, Deliver, Improve. I agree that it describes the Delivery aspect quite well.

[Torben Hagensen, @[email protected] @TMHagensen]

@TotherAlistair and his Heart of Agile boils Agile down to the 4 Words: Collaborate, Reflect, Deliver, Improve. I agree that it describes the Delivery aspect quite well.

[Vaughn Vernon @VaughnVernon]

I think agile comes down to this:

1. Define work that needs to be done
2. Select work that can be done in ~1-3 days (iteration)
3. Determine if that work produced enough value to deploy (increment)
4. Repeat

Issues with this? Even inspect and adapt are there. #KillCeremony

[Dean Peters☕ @deanpeters]

@bakevin @sehlhorst @lissijean IME I've seen #Agile influence the evolution of #prodMgmt positively & negatively.

On the latter, worse case is the cast system that has arisen by attempts to scale by splitting team facing PO vs outward facing PM rather by pairing full stack product people of diff. experience.

[Microservices Weekly @microweekly]

Microservices love Domain Driven Design, why and how? https://t.co/giTdAbpvhq #dddesign #microservices #ddd by @bitboss

[Michael Feathers @mfeathers]

https://t.co/nmTpp13myy

[The Other Alistair @TotherAlistair]

Check it out, the Defense Innovation Board has come up with 6 questions to see whether a project fits the term agile or is "agile BS" ! I'm personally pretty happy with these questions: If you had to change one or more, what would you choose?
https://t.co/9oWiO2JZqm