getInstances.ts

function getInstances<T, C, B> (
  target: T,
  clazz: Class<C>,
  transform: (instance: C) => B = noop
) {
  const transformed: Record<keyof SubType<T, C>, B> = {} as any;
  for (const key in target) {
    const value = target[key];
    if (value instanceof clazz) {
      (transformed as any)[key] = transform(value);
    }
  }
  return transformed;
}

function getInstancesRecursive<T, C, B> (
  target: T,
  clazz: Class<C>,
  transform: (instance: C) => B = noop
) {
  type First = Record<keyof SubType<T, C>, B>; // Instances
  type Second = Record<keyof SubType<T, Record<string, C>>, Record<string, B>>; // Records of instances
  type Double = First & Second;

  const transformed: Double = {} as any;

  // Find the instances
  Object.assign(transformed, getInstances(target, clazz, transform));

  // Find the records of instances
  for (const key in target) {
    const value = target[key];
    if (isPlainObject(value)) {
      (transformed as any)[key] = getInstances(value, clazz, transform);
    }
  }
  return transformed;
}

function noop (val: any) {
  return val;
}

type SubType<Base, Condition> = Pick<Base, {
  [Key in keyof Base]: Base[Key] extends Condition ? Key : never
}[keyof Base]>;

Full Example

type K<Base, Condition> = {
	[Key in keyof Base]: Base[Key] extends Condition ? Key : never
}[keyof Base]

type KR<Base, Condition> = K<Base, Condition> | {
	[Key in keyof Base]: Base[Key] extends object ?
		[KR<Base[Key], Condition>] extends [never] ? never : Key :
		never
}[keyof Base]

interface Crud<A, B, C> {
    a: A;
    b: B;
    c: C;
}

type SubTypeRefMappedCrud<Base> = {
	[Key in KR<Base, Crud<any, any, any>>]: Base[Key] extends Crud<any, any, any> ? Base[Key]['a'] : SubTypeRefMappedCrud<Base[Key]>
}

Usage Example

type A = {
    a: Crud<string, number, string>,
    b: {
        c: Crud<number, number, number>
    }
}

type B = SubTypeRefMappedCrud<A>

let b: B
b.b.c // is type number