Add a is_mapset/1 function to Kernel

Debbie

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Jul 30, 2019, 1:49:31 PM7/30/19

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Hi,

today I needed to assert in a test that something was a mapset. I looked for a is_mapset/1 but I couldnt find one. So I created this one for my test:

def is_mapset(%MapSet{}), do: true

def is_mapset(_), do: false

I was kinda surpised that there is no such function because there are similar functions for all other data types afaik.

Thanks for reading

José Valim

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Jul 30, 2019, 1:54:34 PM7/30/19

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All of the “is_” macros can be used in guards and until Erlang/OTP 21 it was not possible to implement said functionality in a way that is guards compatible. We will drop support for OTP 20 once 1.10 is out (in January) so the proposed feature will exist in Elixir v1.11.

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José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

José Valim

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Jul 30, 2019, 1:55:43 PM7/30/19

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Or to be more precise, we will add is_struct/2, which is a more general feature than the one asked here. There is already an issue tracking this.

Thanks for the proposal!

Norbert Melzer

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Jul 30, 2019, 2:00:10 PM7/30/19

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Due to the opaqueness of `MapSet.t/*` such a macro isn't possible to implement without dialyzer complaining on its usage.

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José Valim

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Jul 30, 2019, 2:09:41 PM7/30/19

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Yes, we had debates about it and it is not the only time Dialyzer would complain. I believe simply pattern matching on %MapSet{} would generate warnings too. The one who has to change here is dialyzer (or Elixir's interface to dialyzer should provide reasonable alternatives for this - although I have no idea which ones).

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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