Swift: netServiceBrowser didRemoveService MacOSX 10.13 - swift

Question

I am trying to run a NetServiceBrowser. It will detect a new ZeroConf device as soon as it appears on the network. It doesn't however detect when the device is removed from the network.
netServiceBrowser(aNetServiceBrowser: NetServiceBrowser!, didRemoveService aNetService: NetService!, moreComing: Bool) is never called.
Am I missing something?
class BonjourDiscovery: NSObject, NetServiceBrowserDelegate, NetServiceDelegate
{
var browser: NetServiceBrowser
var services = [NetService]()
static let instance = BonjourDiscovery()
override init()
{
browser = NetServiceBrowser()
services = []
}
func startDiscovery()
{
browser.delegate = self
browser.searchForServices(ofType: "_smb._tcp.", inDomain: "")
}
func stopDiscovery()
{
browser.stop()
}
func netServiceBrowser(_ browser: NetServiceBrowser, didFind service: NetService, moreComing: Bool)
{
print ("Found:" + service.name)
self.services.append(service)
}
func netServiceBrowser(aNetServiceBrowser: NetServiceBrowser!, didRemoveService aNetService: NetService!, moreComing: Bool)
{
print ("Removed:" + aNetService.name)
if let index = services.index(of: aNetService)
{
services.remove(at: index)
}
}
}

Answer 1

For completeness I have posted the full answer, correcting the didRemoveService function definition (Thanks to Martin R):
class BonjourDiscovery: NSObject, NetServiceBrowserDelegate, NetServiceDelegate
{
var browser: NetServiceBrowser
var services = [NetService]()
static let instance = BonjourDiscovery()
override init()
{
browser = NetServiceBrowser()
services = []
}
func startDiscovery()
{
browser.delegate = self
browser.searchForServices(ofType: "_smb._tcp.", inDomain: "")
}
func stopDiscovery()
{
browser.stop()
}
func netServiceBrowser(_ browser: NetServiceBrowser, didFind service: NetService, moreComing: Bool)
{
print ("Found:" + service.name)
self.services.append(service)
}
func netServiceBrowser(_ browser: NetServiceBrowser, didRemove service: NetService, moreComing: Bool)
{
print ("Removed:" + service.name)
if let index = services.index(of: service)
{
services.remove(at: index)
}
}
}