[erlang-questions] Store maps in ets/dets?

Jesper Louis Andersen <>
Thu Apr 10 18:36:17 CEST 2014


On Thu, Apr 10, 2014 at 6:14 PM, Michael Loftis <> wrote:

> I think you might mean the opposite here....that maps is ephemeral and
> ETS is persistent (or can be persistent using DETS anyway)
>

Actually not. Two things to address though:

Max might have asked if you can store maps in ets:

5> ets:new(foo, [named_table]).
foo
6> ets:insert(foo, {#{a => 3, b => 4}}).
true
7> ets:match_object(foo, '_').
[{#{a => 3,b => 4}}]
8> ets:insert(foo, #{'not' => possible}).
** exception error: bad argument
     in function  ets:insert/2
        called as ets:insert(foo,#{'not' => possible})

and the answer is that you can, but the topmost entry must be a tuple as
the example shows.

The other thing is about persistent vs ephemeral data structures.

http://en.wikipedia.org/wiki/Persistent_data_structure

Maps are persistent, but ETS in general is not. It is ephemeral according
to the wikipedia definition.




-- 
J.
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