[stevebmark]

I would add "Domain Driven Design" - locking your business design in place by trying to make your application match your business structure is a recipe for disaster. If you have a small or stagnant business you probably won't notice any issues. If your business is successful and/or grows, you're going to immediately regret trying to build domains with horrific descriptive names tied to your already obsolete business practices. Instead, design around functionality layers (how we've been doing it for decades, tried and true), and as much as possible keep business logic in config, rows in databases, and user workflows, which makes them extremely flexible.

[eddythompson80]

You'll regret both options. You mentioned the pitfalls of "domain driven design" (outdated language, little code/systems reuse for new endeavors).

However, a highly abstract design with all the business logic in config, workflows, etc will only makes your system extremely flexible as long every one up and down the organization is fairly aware of the abstractions, the config, and uncountable permutations they can take for your business logic to emerge.

Those permutations quickly explode into a labyrinth of unknown/unexpected behaviors what people will rely on. It also makes the cost of onboarding new developers, changing the development team insurmountable. Your organization will be speaking 2 different languages. Most seemingly straightforward "feature asks" that break your abstraction either become a massive system re-design/re-architect or a "let's just hack this abstraction so it's a safer smaller change for now". The former will always be really hard unless you have excellent engineers who have full understanding of the entire system and its behavior and code base along with and excellent engineering practices and processes, and still will take you months or years to pull off. The latter is the more likely to happen and it's why all those "highly abstract, functionality layers, config driven, business logic emerging) projects start perfect and flexible and end up as a "what the fuck is even this".

After a system is implemented, that emergent business logic becomes the language everyone will speak in. Having your organization speaking 2 or 3 completely irreconcilable languages is very painful and unless you have multiple folks up, down and sideways in the organization that can fluently translate between the 2, you'll be in a world of pain and wish you had some closer representation of your domain

[jkaptur]

Along with "make impossible states impossible to represent". If you're designing your types to make a state unrepresentable, you'd better be absolutely sure the state really is impossible for the lifetime of the design.

[wesselbindt]

I don't understand, you're not allowed to change the types? Suppose you disallow any number other than 1, 2, and 3, and you model this with some enum with three members or something. Then you find out that actually a prospective client would love to also work with with the number 4, then you just add 4 to the enum in your next release, no?

[spencerflem]

If its not impossible, you should handle it though.

I think what that quote is against is the common middle ground where states are expected to be 'impossible' and thus not handled and cause bugs when they are found to be not actually.

Either deciding that they are possible or must be impossible is usually better and which one to go with depends on the specifics

[pvillano]

The variant of this I've found useful is to have a separate types for raw/dirty and parsed/validated data