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-module(keydel).
-export([store/3]).
-record(att, {f}).
-type attachment() :: list().
-opaque att() :: #att{} | attachment().
-spec store(atom(), any(), att()) -> att().
store(Field, undefined, Att) when is_list(Att) ->
lists:keydelete(Field, 1, Att);
store(Field, Value, Att) when is_list(Att) ->
lists:keystore(Field, 1, Att, {Field, Value});
store(Field, Value, Att) ->
store(Field, Value, upgrade(Att)).
-spec upgrade(#att{}) -> attachment().
upgrade(#att{} = Att) ->
Map = lists:zip(
record_info(fields, att),
lists:seq(2, record_info(size, att))
),
%% Don't store undefined elements since that is default
[{F, element(I, Att)} || {F, I} <- Map, element(I, Att) /= undefined];
upgrade(Att) ->
Att.
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