Elixir：无法访问struct

Question

I'm trying to get structs to work but none of the documented examples on the Internet or printed books work.

This example on the web site ( https://www.tutorialspoint.com/elixir/elixir_structs.htm ) also shows the same problem:

defmodule User do
   defstruct name: "John", age: 27
end

john = %User{}

#To access name and age of John, 
IO.puts(john.name)
IO.puts(john.age)

I get the error cannot access struct User, the struct was not yet defined or the struct is being accessed in the same context that defines it.

Answer 1

You're probably trying to run this using elixir <filename.exs> while the book you may have seen similar code in was most likely typing the code into iex . (Edit: the code on the page you linked to has been lifted straight from the official tutorial ( http://elixir-lang.org/getting-started/structs.html ) which is typing that code into iex ). This will work in iex but not in an exs script; this is a limitation of the way Elixir "scripts" are compiled and evaluated.

I usually wrap the code in another function (and possibly another module) and invoke that at the end when I have to create and use structs in exs scripts:

$ cat a.exs
defmodule User do
  defstruct name: "John", age: 27
end

defmodule Main do
  def main do
    john = %User{}
    IO.puts(john.name)
    IO.puts(john.age)
  end
end

Main.main
$ elixir a.exs
John
27

Answer 2

Wrapping struct creation and other related operations in a module should be sufficient.

defmodule Customer do
  defstruct name: "", company: ""
end

defmodule BugReport do
  defstruct owner: %Customer{}, details: "", severity: 1
end

defmodule Playground do
  report = %BugReport{owner: %Customer{name: "X", company: "X"}}
  IO.inspect report
end

$ elixir ./your_filename.ex