How to implement TypeScript deep partial mapped type not breaking array properties

Question

Any ideas as to how might apply TypeScript\'s Partial mapped type to an interface recursively, at the same time not breaking any keys with array return types?

The fo

Answer 1

I started with @krzysztof's answer but have since been iterating on it when I come across edge cases. Specifically the edge cases below, based on the given value of the base object (i.e. T[P]):

• any
• any[]
• ReadonlyArray
• Map
• Set

type NonAny = number | boolean | string | symbol | null;
type DeepPartial = {
  [P in keyof T]?: T[P] extends NonAny[] // checks for nested any[]
    ? T[P]
    : T[P] extends ReadonlyArray // checks for nested ReadonlyArray
    ? T[P]
    : T[P] extends (infer U)[]
    ? DeepPartial[]
    : T[P] extends ReadonlyArray
    ? ReadonlyArray>
    : T[P] extends Set // checks for Sets
    ? Set>
    : T[P] extends Map // checks for Maps
    ? Map>
    : T[P] extends NonAny // checks for primative values
    ? T[P]
    : DeepPartial; // recurse for all non-array and non-primative values
};

The NonAny type is used to check for any values