function Observable(subscribe) {
        this._isScalar = false;
        if (subscribe) {
            this._subscribe = subscribe;
        }
    }
@constructor
@param {Function} subscribe the function that is  called when the Observable is
initially subscribed to. This function is given a Subscriber, to which new values
can be `next`ed, or an `error` method can be called to raise an error, or
`complete` can be called to notify of a successful completion.