What is the output of `type Flatten = T extends Array ? U : T` when applied as `Flatten`?

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What is the output of `type Flatten = T extends Array ? U : T` when applied as `Flatten`?

Key points

  • The conditional type `T extends Array ? U : T` checks if `T` is an array.
  • If `T` is an array, it returns `U`.
  • If `T` is not an array, it returns `T`.
  • In this case, `T` is not an array, so the output is `string`.

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