Yeah you bring up a good point. A { name: string } dict needs to be treated differently from a { user_pw: string } dict. The difference is that happens in the domain layer instead of the type layer.

▲ SkiFire13 3 hours ago | parent | next [-]

That's no difference than using newtype structs. If you remove the extra layer you are left with `string` for both of them.

> The difference is that happens in the domain layer instead of the type layer

This view greatly reduces the usefulness of the type layer though, as that's the only automated tool that can help the domain layer with handling cases like this.

	▲	b_e_n_t_o_n 3 hours ago \| parent [-]
		It's not really automated though, it's just another layer of code written by a human, prone to the same types of human error.

▲ valenterry 3 hours ago | parent | prev | next [-]

> The difference is that happens in the domain layer instead of the type layer.

What's those layers you are talking about? In my domain-logic code I use types of course so there is no dedicated "type layer".

▲ RossBencina 2 hours ago | parent | prev [-]

Depending on the language, you can define a PasswordString type that is entirely distinct from the string type. Perhaps it can be explicitly converted to a string (perhaps given a capability token). Then you have:

a { user_pw: PasswordString}

This is what it means to model the domain using types. It is not a separate layer, it is actually using the type system to model domain entities.

▲ b_e_n_t_o_n 2 hours ago | parent [-]

Structurally typed languages can still support information hiding.

   type PasswordString struct {
      pw string
   }
   func(p PasswordString) String(token string) { ... }

I guess the point is that you can model your domain using data as well as types.

▲

lmm an hour ago | parent [-]

> Structurally typed languages can still support information hiding.

But you haven't hidden the information, it's still a string. You can put the string in a wrapper struct but in a structural system that's not really any different from putting it a list or map - the data is still exposed, and if someone writes code to e.g. log objects by just enumerating all their fields (which is a very natural thing to do in those systems) then it will naturally print out your password and there's not really any way to make it ever not.

> I guess the point is that you can model your domain using data as well as types.

You want both in your toolbox though. Restricting yourself to only having types that are essentially lists, maps, or a handful of primitives has most of the same downsides as restricting yourself to not using types at all.

▲

b_e_n_t_o_n an hour ago | parent [-]

You can implement the Stringer interface for the type which prevents it from being logged and since it's private, code from outside of the module can't enumerate it. Of course it's still accessible via reflection or memory dumps etc, but isn't that the case with Java etc? Storing a plain text password like this is a bad idea anyways.

I guess my point is that a structural type system can still allow for encapsulation.

	▲	lmm 16 minutes ago \| parent [-]
		> You can implement the Stringer interface for the type which prevents it from being logged and since it's private, code from outside of the module can't enumerate it. Those sound like decidedly non-structural features. And couldn't you undermine them by passing it to a function that expects a different `struct { pw string }` and logs its contents?