         deviceList.numberOfDevices = UInt16(HCI.maximumDeviceCount)
         
         // request device list
-        let ioctlValue = withUnsafeMutablePointer(to: &deviceList) {
-            IOControl(fileDescriptor, HCI.IOCTL.GetDeviceList, $0)
-        }
-        guard ioctlValue >= 0 else { throw POSIXError.fromErrno() }
+        guard withUnsafeMutablePointer(to: &deviceList, {
+            IOControl(fileDescriptor, HCI.IOCTL.GetDeviceList, $0) >= 0 })
+            else { throw POSIXError.fromErrno() }
         
         return deviceList
     }

    }
}

// MARK: - Supporting Types

internal extension HostController {

            else { throw POSIXError.fromErrno() }
    }
    
    /// Close the HCI device.
    func disable(_ identifier: HostController.Identifier) throws {
        
        guard IOControl(fileDescriptor, HCI.IOCTL.DeviceDown, CInt(identifier)) >= 0
            else { throw POSIXError.fromErrno() }
    }
    
    /// Get device information.
    func deviceInformation(_ identifier: HostController.Identifier) throws -> HCIDeviceInformation {
        
