Mapped types distribute as well

mappedTypesDistribute.ts

type Nodes =
  | {
      type: "a";
      age: number;
    }
  | {
      type: "b";
      size: string;
    };

type Validation<T> = {
  // T is naked
  [P in keyof T]: boolean;
};

type R = Validation<Nodes>;
// Validation<{ type: "a"; age: number; }> | Validation<{ type: "b"; size: string; }>
//
// Nodes is an union of types && mapped type is homomorphic 
// => the mapped type distributes over the constituents of the union
// => the result is the union of the resulting mapped types