No. 238 · August 21, 2026 · Brutal
UnionToIntersection
Implement `UnionToIntersection<U>` so `A | B` becomes `A & B`. There is no operator for this — the answer exploits how the compiler infers from function parameters.
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Puzzle
Par 5Puzzle
union-to-intersection.tsStroke 1 of 5Not run yet
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Checks
4UnionToIntersection<{ a: string } | { b: number }>—→ { a: string } & { b: number }UnionToIntersection<string>—→ stringUnionToIntersection<'a' | 'b'>—→ neverUnionToIntersection<{ x: 1 }>—→ { x: 1 }
How a check is judged Exact type equality, not assignability — an intersection is not the same as the flattened object.
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Short game
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02
Annotated solution
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