[eyelidlessness]

> But let’s dissect that last suggestion; suppose I do modify the type to encode that. Suddenly pretty much every field more or less just because Maybe/Optional. Once everything is Optional, you don’t really have a “type” anymore, you have a a runtime check of the type everywhere. This isn’t radically different than regular dynamic typing.

Of course it’s different. You have a type that accurately reflects your domain/data model. Doing that helps to ensure you know to implement the necessary runtime checks, correctly. It can also help you avoid implementing a lot of superfluous runtime checks for conditions you don’t expect to handle (and to treat those conditions as invariant violations instead).

[tombert]

No, it really isn’t that different. If I had a dynamic type system I would have to null check everything. If I have declare everything as a Maybe, I would have to null check everything.

For things that are invariants, that’s also trivial to check against with `if(!isValid(obj)) throw Error`.

[dwb]

Sure. The difference is that with a strong typing system, the compiler makes sure you write those checks. I know you know this, but that’s the confusion in this thread. For me too, I find static type systems give a lot more assurance in this way. Of course it breaks down if you assume the wrong type for the data coming in, but that’s unavoidable. At least you can contain the problem and ensure good error reports.

[eyelidlessness]

The point of a type system isn’t ever that you don’t have to check the things that make a value represent the type you intend to assign it. The point is to encode precisely the things that you need to be true for that assignment to succeed correctly. If everything is in fact modeled as an Option, then yes you have to check each thing for Some before accessing its value.

The type is a way to communicate (to the compiler, to other devs, to future you) that those are the expected invariants.

The check for invariants is trivial as you say. The value of types is in expressing what those invariants are in the first place.

[the-grump]

You missed the entire point of the strong static typing.