No. 219 · July 27, 2026 · Gentle

Rebuild Partial

Implement `MyPartial<T>` so every property becomes optional. Making the value accept `undefined` is not the same thing — the key itself has to become optional.

Puzzle

Par 2

Puzzle

rebuild-partial.ts

interface User {
  id: number
  name: string
}

type MyPartial<T> = ???

type MyPartial<T> = ???

Stroke 1 of 2Not run yet

Replace ??? — your solution is checked against the cases below.

Checks

MyPartial<User>—
→ { id?: number; name?: string }
MyPartial<{ a: string }>—
→ { a?: string }
MyPartial<{}>—
→ {}

How a check is judged Exact type equality, not assignability — an intersection is not the same as the flattened object.

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Annotated solution

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