[erlang-questions] small post about ordered_set and partially-bound keys

[Andreas Schultz]

Max Lapshin <max.lapshin@REDACTED> schrieb am Do., 13. Dez. 2018 um
10:06 Uhr:

> Erlang ets with ordered_set mode has very cool feature: partially bound
> tuple primary key that allows to use ets as a good old binary tree.
>
> I haven't found any good explanations of how to use, so have written some
> draft of post:
>
> https://medium.com/@max.lapshin/how-we-adopted-partial-ordered-set-in-erlang-782f773349f4
>

You don't need to play tricks with ets:fun2ms/1. It is mostly a helper so
that you don't have to think to much about the structure of a match spec
yourself. But, you can still construct the same spec manually.

So, instead of:

    ets:fun2ms(fun (#segment{utc={_,_,_}} = Segment) ->  true end)

You can simply use:

    [{#segment{utc = {'_','_','_'}, _ = '_'}, [], [true]}]

Or to use your sample:

    match_spec_hour(Name, Hour, true) ->
     [{#segment{utc = {Name,Hour,'_'}, _ = '_'}, [], [true]}];

    match_spec_hour(Name, Hour, segment) ->
     [{#segment{utc = {Name,Hour,'_'}, _ = '_'}, [], ['$_']}].

Regards
Andreas


>
> Would be glad for any feedback.
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