If you are building a web scraper that follows links, you might need to be aware of which pages you've already visited. It's quite possible that a page you are visiting contains a link to a page you have already visited, sending you into an infinite loop. Therefore, it is very important to build a tracking system into your scraper that records its history.
The simplest data structure for storing a unique collection of items would be a set. The Go standard library does not have a set data structure, but it can be emulated by using a map[string]interface{}{}.
In Go, you can define a map as follows:
visitedMap := map[string]interface{}{}
In this case, we would use the visited URL as the key, and anything you want as the value. We will just use nil, because as long as the key is present...
