I find it kinda odd that a fundamental principle of OOP is information hiding, yet most mainstream languages make it a matter of pure discipline if you want to pass around a "CustomerId" instead of an "Int32" or alias any value type. In your own code it's not too bad, but there's constant conversions at api and library boundaries...

In general I lack the Smalltalk ideal of being able to subclass any type, like 'Int', call it something new and attach behaviour to it, while preserving API & DB compatibility.

Type aliasing in F#, ie `type Customer = int`, or discriminated unions with the same info, like `type CustomerId = CustomerId of int`, are wonderfully useful in that regard.