Proposal: Support of ETS guard conditions for Registry.match/3

[Yurko Hoshko]

Hello everyone.

There is a small proposal for improvement in Registry.match/3 .

At the moment it does not support ETS guard conditions, which could be quite useful.

Current behavior:

  @spec match(registry, key, match_pattern :: atom() | tuple()) :: [{pid, term}]
  def match(registry, key, pattern) when is_atom(registry) do
    spec = [{{key, {:_, pattern}}, [], [{:element, 2, :"$_"}]}]

    ...
  end

Second element of spec list is a list of guards which is empty and non-changeable at the moment.

What we could do instead is allow passing additional guards for more precise lookup.

So it would be something like:

  @spec match(registry, key, match_pattern :: atom() | tuple(), guards :: list()) :: [{pid, term}]
  def match(registry, key, pattern, guards \\ []) when is_atom(registry) and is_list(guards) do
    spec = [{{key, {:_, pattern}}, guards, [{:element, 2, :"$_"}]}]

    ...
  end

Example of guard list for checking if pattern variable is greater then 1: 

[{:>, :"$1", 1}]

It is a bit ugly syntax though - so it would be nice to hear if someone has better ideas to do, as well as is this feature useful at all.

Thanks :)

P.S. Link to Registry.match/3 on GitHub: GitHub

[christ...@gmail.com]

I actually came to the forum to start a discussion on match specs in Elixir before noticing your post well before the my daily digest was issued, if you're interested.

[José Valim]

Hi Yurko, please send a pull request that adds support for guards. :)

In the documentation we should make it clear that only the matchspec variables $1, $2 and friends must be used. If you use $$ or $_ there is no guarantee the representation will be kept.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Yurko Hoshko]

Will prepare PR with functionality and documentation updates and post it as WIP once it is ready.

пʼятниця, 24 лютого 2017 р. 12:14:10 UTC+2 користувач José Valim написав:

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