Update a struct field

# Define a struct for this example
defmodule User do
  defstruct email: nil
end

%User{email: "[email protected]"} = struct(%User{}, email: "[email protected]")

# Structs are based on maps
# so map update methods and syntax are valid
%User{email: "[email protected]"} = %{ %User{} | email: "[email protected]" }

%User{email: "[email protected]"} = Map.put(%User{}, :email, "[email protected]")