Dot (.) operator with pipe operator

Is there any way to leverage the pipe operator to access properties of an object after a sequence of operations?

I’m trying to do a sequence of operations followed by accessing a property in the final map but I can’t get it to work while making it look great

Here’s what I have:

hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills
  |> Enum.at(pill_ix)
  |> &(&1.pill_id)

ElixirLS autocorrects this to

hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills
  |> Enum.at(pill_ix)
  |> (& &1.pill_id)

and that does not work, it throws the following error:

(ArgumentError) cannot pipe Enum.at(
  hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills,
  pill_ix
) into & &1.pill_id, can only pipe into local calls foo(), remote calls Foo.bar() or anonymous function calls foo.()

This makes me think it’s not possible, but there’s no harm in asking because it still feels like something with a trivial solution. The alternative would be doing this:

(hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills
  |> Enum.at(pill_ix)).pill_id

but this way makes me have to add an extra parenthesis to the front, which is a bit ugly in my opinion because in the case I have to do it several times it will accumulate a lot of parenthesis in the front, plus I’ll have to go back and forth adding them.

Any insights into this? Thanks!

If you wanted to do it like this, you would need to write

  |> Enum.at(pill_ix)
  |> (&(&1.pill_id)).() # You need the parentheses to make it a function call

but in the latest Elixir you can also use

  |> Enum.at(pill_ix)
  |> then(& &1.pill_id)

which you may prefer. Or you might use foo = <your_pipe> and then foo.pill_id.

3 Likes

Why not use Map.fetch!/2?

hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills
  |> Enum.at(pill_ix)
  |> Map.fetch!(:pill_id)
1 Like

The leading parenthesis is the only thing you have a problem with in that expression? :stuck_out_tongue:

The short answer for your question is then, as noted by others. But I’d recommend you consider identifying and naming these complex operations better. For instance:

hd(hd(ctg).tier_group.tiers_in_tier_group).tier.tier_pills
  |> Enum.at(pill_ix)

could be:

def pill_at(x, idx) do
  Enum.at(hd(x.tier_group.tiers_in_tier_group).tier.tier_pills, idx)
end

and then your pipe is shorter / gone:

pill_at(hd(ctg), pill_ix).pill_id
1 Like

ohhh alright, thanks a lot! I’ll probably go with the then notation since it looks the cleanest in this scenario

That’s another way, thanks!

Yeah it most definitely needs some refactoring but I was just trying to get something to work since I more often than not have to end up changing what I wrote hahaha