CODEWITHSUNDEEP
elixirlist-comprehensionelixir-mixex-unit
J du Preez
J du Preez

Reputation: 145

Elixir List Comprehension to Create a New List of Structs

I'm quite new to Elixir, and trying to yield a new list of structs using list comprehension, and for the life of me I can't seem to get this right:

holdings = ServiceX.update_holdings(
         fn() -> for n <- 1..3, do: n end,
         &(for n <- 1..100, do: %Holding {
                                  client_id: &1,
                                  company_id: n,
                                  company: "---",
                                  revenue: 0.0 }
         ))

update_holdings takes in another function that returns a list of of structs. The real implementation calls out to the database. This code is for an ExUnit test, where I'm trying to return some stubbed data.

Seems I'm getting something obvious wrong here. Here's the error I get when I run: mix test

** (Protocol.UndefinedError) protocol Enumerable not implemented for 
   %Holding{client_id: 1, company: "---", company_id: 1, revenue: 0.0}

So am I missing a module import, or how else do I produce a list of structs using list comprehension?

Upvotes: 0

Views: 465

Answers (1)

J du Preez
J du Preez

Reputation: 145

Incorrect code:

def update_holdings(f1, f2) do
     ids = f1.()
     for id <- ids,
         holdings <- f2.(id),
         holding <- holdings,
         do: holding
 end

The problem is the extra nested enumeration holding <- holdings. This is a amateur mistake because I misunderstood how it works in Elixir. Changing the above to the following fixed the problem:

def update_holdings(f1, f2) do
     ids = f1.()
     for id <- ids,
         holding <- f2.(id),
         do: holding
 end

Upvotes: 0

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