Phoenix.Component slot attributes cannot accept the :default option - is there a reason for this?

Phoenix Forum Questions / Help
1

Unlike attributes, slot attributes cannot accept the :default option. Passing one will result in a compile warning being issued.

Is there a technical reason for this? I find myself wanting for this feature. Is it just work that hasn’t been done yet or is there a technical issue preventing it? Or is it a bad idea for some reason?

2

I don’t have an answer to your question around the technical limitations but since a an empty slot is passed in as an empty list I do this:

slot :bar

def foo(assigns) do
  ~H"""
  <%= if Enum.any?(@bar) do %>
    <%= render_slot(@bar) %>
  <% else %>
    Default
  <% end %>
  """
end

I literally just did this the other day and would likely use it sparingly (and may try and come up with a different solution that doesn’t need a default). You might want to capture the slot’s empty state in an assign as I haven’t fully wrapped my head around when it’s ok to use a function in heex (and I’m currently seeing some extra data being sent): assigns = assign(assigns, :bar_empty?, Enum.empty?(assigns.bar)).

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3

This is what I do:

<%= if @bar == [] do %>
    Default
  <% else %>
    <%= render_slot(@bar) %>
<% end %>
4

I’m talking about slot attributes…

slot :bar do
  attr :foo, :string, default: ""
end

Will give a compiler warning because default values on slot attributes aren’t allowed (like they are on regular component attributes).

You can kinda work around it by doing this…

~H"""
  <%= for bar <- @bar do %>
    <% bar = Map.put_new(bar, :foo, "") %>
    ...
    <%= render_slot(bar) %>
  <% end %>
"""

But it’s kinda wonky and not very clear.

1 Like
5

Oh, right :joy: :joy: :joy: :joy: I swear I’ve written code before…

Ohhhhhh, well ain’t my response just one pile of mistakes :joy:

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6

I misunderstood the question just like you! :laughing:

1 Like
7

Yes, I am concerned it will be slow in practice. We would need to traverse the slot attributes and then every child to set the default. At the root it is not a concern because it is a direct operation on attrs.

4 Likes