How to write a function that can either take an argument or default to set value?

Phoenix Forum Questions / Help
1

I’m trying to write a function that can either take an argument or default to set value.

  def live_view(opts \\ []) do
    layout = opts[:layout] || {AppWeb.Layouts, :app}
    container = opts[:container] || {:div, class: "flex min-h-svh"}
    quote do
      use Phoenix.LiveView,
        layout: unquote(layout),
        container: unquote(container)

      unquote(html_helpers())
    end
  end

I’ve tried this, but I get an error stating:

** (UndefinedFunctionError) function AppWeb.live_view/0 is undefined or private.
2

To answer your question, one approach can be the multi arity approach:

def live_view() do
  live_view([{AppWeb.Layouts, :app}, {:div, class: "flex min-h-svh"}])
end

def live_view(opts) do
    layout = opts[:layout]
    container = opts[:container]
    quote do
      use Phoenix.LiveView,
        layout: unquote(layout),
        container: unquote(container)

      unquote(html_helpers())
    end
end

Maybe you can share your goal also?

3

To be able to help I think we’d need to see where you are calling your function from - not just where it’s defined.

From my reading of the code (returning AST from function, rather than a macro), you’re intending this function to be used at compile time. The error may well result from the module AppWeb not being compiled at the time you’re trying to call a function on it.

4

live_view is called from

defmodule AppWeb.UserLoginLive do
  use AppWeb, :live_view
end

I’m not quite sure how I’m going to pass the arguments, my intention was for the function to be called the same way as Phoenix.LiveView, inside the live.

5

Not a direct answer, but you can customize the layout from the mount callback:

def mount(_, _, socket) do
  {:ok, socket, layout: …}
end

No need to do that via the use Phoenix.LiveView call.

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