> if your code is full of bespoke types that are only relevant to a couple of places where they're used, you hurt interoperability; you lock yourself in to how

> if your code is full of bespoke types that are only relevant to a couple of places where they're used, you hurt interoperability; you lock yourself in to how things are done now; and you may just be shifting the burden of making sense to someplace else in the code What is an example of bespoke types? Is is all compound types (structs, classes)? If you need interop or extensibility, make an API. Feel free to use whatever types in your library you want, just make sure to agree to the API interface. I’m honestly not sure what style of programming you are advocating for einpoklum. Can you provide an example? All non-primitive types are essentially n-ary trees of types of sub-members (ignoring unions) with primitive types as leaves. Passing your non-primitive type so some external library function is accomplished by the library declaring that the type it receives must adhere to an interface.