[SideburnsOfDoom]

> While true, if your language doesn’t support such a type

You'd be surprised where the support is. In C#, you would declare a struct type with one read only field of type double, and range validation (x <= x <= 1) in the constructor.

this is the "value object" pattern. http://wiki.c2.com/?ValueObject

Yes there's a bit of boilerplate - especially since you might want to override equality, cast operators etc. But there is support. And with a struct, not much overhead to it.

[kaoD]

I don't think runtime validation is that special. You can bend most languages into this pattern one way or another. The real deal is having an actual compile-time-checked type that resembles a primitive.

[SideburnsOfDoom]

Actually what I want is just the reading experience of seeing

"public Customer GetById(CustomerId id)" instead of "public Customer GetById(string id)" when only some strings (e.g. 64 chars A-Z and 1-9) are valid customer ids.

Compile-time validation would be ideal, but validation at the edges, well before that method, is good enough.

[SideburnsOfDoom]

See: "Primitive Obsession" https://wiki.c2.com/?PrimitiveObsession

Usually cured by using Value objects. I wish this done more in OO code.

Could it be better supported in these languages? Yes, for sure. But is it true that "these language do not support such a type" at all? No.