It delegates part of that responsibility to plug and this function:

https://github.com/elixir-plug/plug/blob/master/lib/plug/router/utils.ex#L52-L67

The primary logic starts here:

https://github.com/phoenixframework/phoenix/blob/master/lib/phoenix/router.ex#L321-L324

The thing that generates the final AST is here:

https://github.com/phoenixframework/phoenix/blob/master/lib/phoenix/router.ex#L353-L386

My understanding is that it effectively turns into something like:

def __match_route__(conn, :get, ["users", id], "www.google.com")

That means, when it initially gets a request, it just splits the path by / and can then match on that.

Thanks, I was hoping I wouldn’t have to take a deep dive into the source but in order to understand what’s going on under the hood looks like I have no choice.

simplified, we generate function heads like this:

def match(conn, "GET", ["users"]), do: UserController.call(conn, UserController.init(:index))
def match(conn, "GET", ["users", id]) do
  new_params = Map.merge(conn.params, %{"id" => id})
  UserController.call(%{conn | params: new_params}, UserController.init(:show))
end
def match(conn, _, _) do: # raise Phoenix.NotFoundError ...

Hey Chris thanks, that really pointed me in the right direction. I dug a little deeper and found this video Erlang Factory 2014 – Write Less, Do More (and Have Fun!) with Elixir Macros The video is a gem and really helped me understand Macros.

I was always curios how the Router layer worked in Phoenix. For any one interested about 31:22 Chris explains how routes work. I also purchased Metaprogramming Elixir, used my Elixir Forum discount and got it for 7 bucks. What a steal!