BidirAssoc

. . . Technique for bidirectional associations.

Bidirectional construction

Say each of two objects links to the other one, you may want to have code as the following,

a0 = %A{hello: b0}
b0 = %B{world: a0}

You found that it does not work. Do not be frustrated. Do not give up using functional programming.

And this project tends to give a better approach on functional programming.

Say those elements exist, including macro ref/2 for object-reference definition, function get_ref/2 for object-reference retrieval, and both object modules BidirAssoc.A and BidirAssoc.B.

import BidirAssoc, only: [ref: 2, get_ref: 2]
alias  BidirAssoc.A
alias  BidirAssoc.B

First you have to construct basic sturcts, then combine them into a magic binary construction.

a0 = %A{value: :hello}
b0 = %B{value: :world}
a =
  quote(do: ref(unquote(a0), unquote(b0)))
  |> Macro.expand_once(__ENV__)

And it seems like that.

%BidirAssoc.A{
  hello: {:ref, [],
   [
     %BidirAssoc.B{value: nil, world: nil},
     %BidirAssoc.A{hello: nil, value: nil}
   ]},
  value: :hello 
}

And you may want to start from a, the structure %BidirAssoc.A{}, and go down to a.hello that's a structure %BidirAssoc.B{}, and a.hello.world, %BidirAssoc.A{}, and a.hello.world.hello, %BidirAssoc.B{}, and so on.

a                               # This is a `%BidirAssoc.A{}`.

a |> BidirAssoc.get_ref(:hello) # This is a `%BidirAssoc.B{}`.

a
|> BidirAssoc.get_ref(:hello)
|> BidirAssoc.get_ref(:world)   # This is a `%BidirAssoc.A{}`.

a
|> BidirAssoc.get_ref(:hello)
|> BidirAssoc.get_ref(:world)
|> BidirAssoc.get_ref(:hello)   # This is a `%BidirAssoc.B{}`.