Why can I pass a struct to the route path helper?

Hello :wave:

In the router.ex file, I have the following route:

resources "/users", UserController

In a Controller, I can use the route path helper:

redirect(to: Routes.user_path(conn, :show, user))

Why does it work? user is a struct, but the path/url will contain an id.

Have a look here https://hexdocs.pm/phoenix/routing.html#path-helpers

In the examples, primitives are passed, e.g.
HelloWeb.Router.Helpers.user_post_path(Endpoint, :show, 42, 17)

So that doesn’t explain why structs can be passed.

They are functions that accepts structs and converts them

Scroll down to helpers comment and examine the functions you will see conn structs and endpoints structs


In particular…

      defp to_param(int) when is_integer(int), do: Integer.to_string(int)
      defp to_param(bin) when is_binary(bin), do: bin
      defp to_param(false), do: "false"
      defp to_param(true), do: "true"
      defp to_param(data), do: Phoenix.Param.to_param(data)

With pattern matching (and guards) it is simple to extract id from struct, or any…


Thank you! This is where the code tries to find the value from the struct:

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You are welcome, glad I could help