     }
 
     /// Returns the bits of `self` shifted once toward `direction`.
-    @warn_unused_result(mutable_variant="shiftOnce")
-    public func shiftedOnce(toward direction: ShiftDirection) -> Bitboard {
+    @warn_unused_result(mutable_variant="shift")
+    public func shifted(toward direction: ShiftDirection) -> Bitboard {
         switch direction {
         case .North:     return  self << 8
         case .South:     return  self >> 8

    }

    /// Shifts the bits of `self` once toward `direction`.
    public mutating func shiftOnce(toward direction: ShiftDirection) {
        self = shiftedOnce(toward: direction)
    }

    /// Returns the bits of `self` filled toward `direction` blocked by `blockers`.


    /// Returns the attacks available to the king in `self`.
    internal func _kingAttacks() -> Bitboard {
        let attacks = shifted(toward: .East) | shifted(toward: .West)
        let bitboard = self | attacks
        return attacks
            | bitboard.shifted(toward: .North)
            | bitboard.shifted(toward: .South)
    }

    /// Returns the attacks available to the knight in `self`.
