[Feature proposal] @enforce_keys should accumulate

[Krzysztof Wende]

In case we want to define a macro that requires some keys from the struct, @enforce_keys should have `accumulate: true`

Otherwise we cannot require some fields from a structures in multiple places.

We could use 

```

quote do

    @enforce_keys [:key] ++ (Module.get_attribute(__MODULE__, :enforce_keys) || [])

end

```

in __using__

But this way if we do `use` before our own @enforce_keys the key will get overwritten.

If we allowed that to accumulate we could do @enforce_keys many time still respecting all of them

[José Valim]

This is tricky because I can see someone using @enforce_keys to define a default value and they may want to override it later on.

I think there is no right answer but given there is a cost of change, I would suggest to keep the behaviour as is.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Allen Madsen]

You'd have to try this out, but it might work to add the additional enforced keys in __before_compile__ instead.

Allen Madsen
http://www.allenmadsen.com

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