Strongly depends on the language. If you have ML style data types (eg ML, Haskell, OCaml, Rust) ands some way to abstract types (ML structs, Haskell modules hid

Strongly depends on the language. If you have ML style data types (eg ML, Haskell, OCaml, Rust) ands some way to abstract types (ML structs, Haskell modules hiding type constructors, OCaml modules, Rust modules) then it is generally possible to design your data structures in such a way that invalid states cannot be represented. If a user has an optional first/last name but if one is specified then so is the other, your user type has a name of type (eg) Maybe (string, string) [1]. If your deserialisation framework just fills in default values for everything or let’s you have unused fields then it is, in my opinion, broken. If you have a field that should be a positive bumber, you should have a type for a positive number that fails to deserialise if you give it a negative number. [1] the caveat is that it somewhat sucks to change these restrictions and therefore the types. Compilers can hopefully make these refractors easier, but they may still suck. In languages like clojure, you mostly have to try to write programs/tests to be resilient to any reasonable changes to the data structures that you can imagine.