From: "austin (Austin Ziegler) via ruby-core" <ruby-core@...>
Date: 2023-05-19T16:23:31+00:00
Subject: [ruby-core:113533] [Ruby master Feature#19634] Pattern matching dynamic key

Issue #19634 has been updated by austin (Austin Ziegler).





I count 44 instances of this in our production code (~100k lines of Elixir), but I don���t think I���ve ever used key and value pinning as shown in the examples above.



But dynamic key matching is precisely what is required when it is required, although it���s rare enough.



Here's a sample GraphQL response parser or the Shopify Customers API:



```elixir

  def parse_customer_response(%{} = body, resource, action) do

    gql_action = resource <> String.capitalize(action)



    case body do

      %{status: 200, body: %{^gql_action => %{^resource => %{} = result, "userErrors" => []}}} ->

        {:ok, result}



      %{status: 200, body: %{^gql_action => %{"userErrors" => []} = result}} ->

        {:ok, result}



      %{errors: errors} ->

        {:error, Enum.map(errors, &Map.get(&1, "message"))}



      %{body: %{^gql_action => %{"userErrors" => errors}}} ->

        {:error, Enum.map(errors, &Map.get(&1, "message"))}



      %{body: %{^gql_action => nil}} ->

        {:error, [%{message: "#{gql_action} access denied"}]}



      %{body: nil} ->

        {:error, [%{message: "#{gql_action} access denied"}]}



      _ ->

        {:error, [%{message: "Unknown error"}]}

    end

  end

```



I haven���t started using pattern matching in Ruby, but I could see some simplified code with dynamic key matching.



(As a separate note, it appears that email replies to redmine aren���t necessarily working, as this should have come in by email.)



----------------------------------------

Feature #19634: Pattern matching dynamic key

https://bugs.ruby-lang.org/issues/19634#change-103160



* Author: baweaver (Brandon Weaver)

* Status: Open

* Priority: Normal

----------------------------------------

I found myself in a situation ([stable marriage problem](https://rosettacode.org/wiki/Stable_marriage_problem#top-page)) where I would like to match against a dynamic key, like so:



```ruby

mentor_proposals = { mentor_name: ['mentee_1', 'mentee_2'] }

mentor_name = :mentor_name

mentee_name = 'mentee_1'



mentor_proposals in ^key: [*, ^mentee_name, *] # SyntaxError

```



Currently this is not supported syntax, but there are some use cases in which I might see myself wanting to use it including this one. As `deconstruct_keys` currently accepts an `Array` of keys this would not break compatibility but would introduce syntactic complexity in capturing keys on hash-like matches.



I believe the tradeoff is worthwhile, but would like to hear others opinions on the matter.



Granted this case has some oddities of `Symbol` and `String` interchangeability as an implementation detail, and I will not be arguing for key irreverence in this issue as that's a [much more involved topic](https://dev.to/baweaver/the-case-for-pattern-matching-key-irreverence-in-ruby-1oll).







-- 

https://bugs.ruby-lang.org/

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