Pair<A,B>, Nominal Tuples and Variadic Generics

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5

Not necessarily.

struct Void {
  init() {}
}
struct Tuple<First, Rest> {
  var first: First
  var rest: Rest
}

Then make () sugar for Void, (T, U) sugar for Tuple<T, U>, (T, U, V) sugar for Tuple<T, Tuple<U, V>>, etc. This design lends itself to recursive definitions of protocol conformances:

extension Void: Equatable {
  static func == (lhs: Void, rhs: Void) -> Bool {
    return true
  }
}
extension Tuple: Equatable where First: Equatable, Rest: Equatable {
  static func == (lhs: Tuple, rhs: Tuple) -> Bool {
    return lhs.first == rhs.first && lhs.rest == rhs.rest
  }
}
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