I'm just a user but: • if you've used Spring, middleware are Filters • - • https://github.com/metosin/reitit/blob/master/doc/ring/coercion.md • bidirectional routing lets you convert from a path to a route, and the reverse, see https://github.com/metosin/reitit/blob/master/doc/README.md • see https://github.com/metosin/reitit/blob/master/doc/faq.md for comparison with other routing libraries, but also this table on bidi https://github.com/juxt/bidi#comparison-with-other-routing-libraries

“Coercion is separate from routing” means (to me), among other things, that routing is data driven, and you can define your coercion needs also with data, but coercion itself requires the execution of a function to carry out your wishes, so it requires middleware to pull it off.

Bidirectional routing means you can match a path to a route and also match a route to a path. What this means concretely is the following.

(require '[reitit.core :as r])

(def routes
  [["/" :index]
   ["/metrics" :metrics]])

(def router (r/router routes))

(r/match-by-path router "/metrics") ;=> {:template "/metrics", :path "/metrics", :data {:name :metrics}, ...}
(r/match-by-name router :metrics)   ;=> {:template "/metrics", :path "/metrics", :data {:name :metrics}, ...}

As for what reitit brings to the table: it brings routing and nothing else. Reitit is a routing library, whereas Ring is an abstraction of HTTP requests and responses. The way it works with Ring is as follows: • User requests resource • Ring defines a way to represent HTTP requests and responses as data • In particular, a Ring adapter transforms HTTP requests sent to a web server into a Clojure map • This map contains a URL, and the URL gets passed to Reitit to find a route • Once a route is found, we can use the data of the route to figure out what to do next (e.g. handle the HTTP request) • Your HTTP request handler is a function that returns a response map

@U0479UCF48H thank you very much, really detailed explanation 🙌