Re-initialize a lazy initialized variable in Swift

lazy is explicitly for one-time only initialization. The model you want to adopt is probably just an initialize-on-demand model:

var aClient:Client {
    if(_aClient == nil) {
        _aClient = Client(ClientSession.shared())
    }
    return _aClient!
}

var _aClient:Client?

Now whenever _aClient is nil, it will be initialized and returned. It can be reinitialized by setting _aClient = nil