Today I Learned

A Hashrocket project

Ready to join Hashrocket? Find Openings here and apply today.

Aliasing an Elixir Module Within Itself

I was attempting to compile a Phoenix application and I got this error:

Post.__struct__/0 is undefined, cannot expand struct Post

The issue was in a function I defined in the module.

def changeset(%Post{}= post, attrs \\ %{}) do
    ...
end

I assumed that you would get references to a module within said module for free. That’s not the case. There are two ways to fix the error. One is to use the full module name in the parameter list.

def changeset(%Forum.Post{}= post, attrs \\ %{}) do
    ...
end

Alternatively, I can alias the module within itself.

alias Forum.Post
Looking for help? At Hashrocket, we 💜 Elixir! From our many Elixir client projects, to sponsoring the Chicago Elixir Meetup, to the source code for this application, we are invested in this community. Contact us today to talk about your Elixir project.