BFE.dev solution for TypeScript puzzle
1. implement Partial<T>

From the description, we see that the goal is to make every property optional for an object.

type Foo = {  a: string  b: number  c: boolean}

MyPartial<Foo> should be

type PartialFoo = {  a?: string  b?: number  c?: boolean}

We need to map each property to its optional form. Mapped Types comes in handy.

type MyPartial<T> = {    [P in keyof T]?: T[P]}

keyof T holds all the property keys of T, [P in keyof T] is to iterate over all of them. And it maps each key to T[P] which is the value type. Notice the use of ? to make keys as optional.