I’d like to challenge that claim.

defmodule Foo do
  defstruct [:foo, :bar]

  @foos File.read!("lib/foos.json")
        |> Jason.decode!(keys: :atoms)
        |> Enum.map(&Map.put(&1, :__struct__, __MODULE__))

  def list do
    @foos
  end

  def equal? do
    @foos == [%Foo{bar: 2, foo: 1}, %Foo{bar: 22, foo: 11}]
  end
end

Foo.list() |> IO.inspect(label: "list()")
Foo.equal?() |> IO.inspect(label: "equal?()")

So you can’t use the struct function but that’s a small price to pay if you really want/need to do this.

The first is just a dump alias for the current module name. The second is creating a struct, which does do things like checking keys, and such, which does fail without the struct being defined.

&Map.put(&1, :__struct__, __MODULE__) just uses knowledge about implementation details of structs to construct them without doing all the consistency checks structs have when being constructed otherwise.