gistfile1.txt

#
# library part
#
 
defprotocol PerxistentProto do
   def refresh o
   def save! o
end
 
defmodule Perxistent do
   defmacro __using__(_) do
      quote do
         def save! o do
            o |> Perxistent.Storage.put
            o
         end
 
         def refresh o do
            Perxistent.Storage.get __MODULE__, o.id
         end
      end
   end
   defmacro object type do
      quote do
         defimpl PerxistentProto, for: unquote(type) do
            def refresh o do unquote(type).refresh o end
            def save! o do unquote(type).save! o end
         end
      end
   end
   def refresh o do PerxistentProto.refresh o end
   def save! o   do PerxistentProto.save! o end
   def load type, id do Perxistent.Storage.get type,id end
end
 
#
# client part - persistent object definition and storage implementation
#
 
require Perxistent
 
## implement persistent object
defmodule Person do
   defstruct id: nil, name: "", surname: ""
 
   use Perxistent
end
Perxistent.object Person
 
## implement storage
defmodule Perxistent.Storage do
   def put o do
      IO.puts "STORAGE: should store object #{inspect(o)}"
   end
 
   def get type, id do
      IO.puts "STORAGE: should load object of type #{inspect(type)} and id #{inspect(id)}"
   end
end
 
#
# client part - usage
#
 
# create object
o = %Person{id: :someid, name: "Miroslav", surname: "Prýmek"}
 
# save it
o = Perxistent.save! o
 
# modify it locally
o = o |> Map.put(:x,:x)
 
# refresh saved state
o = Perxistent.refresh o
 
# load object with id :someid from storage 
o = Perxistent.load Person, :someid