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Construct a copy of a different cancellation slot wrapper type.
template< typename U, typename OtherCancellationSlot> cancellation_slot_binder( const cancellation_slot_binder< U, OtherCancellationSlot > & other, constraint_t< is_constructible< CancellationSlot, OtherCancellationSlot >::value > = 0, constraint_t< is_constructible< T, U >::value > = 0);
            This constructor is only valid if the CancellationSlot
            type is constructible from type OtherCancellationSlot,
            and the type T is constructible
            from type U.