From: ruby-core@...
Date: 2016-12-28T19:54:01+00:00
Subject: [ruby-dev:49929] [Ruby trunk Feature#13067] TrueClass, FalseClass to provide `===` to match truthy/falsy values.

Issue #13067 has been updated by Marc-Andre Lafortune.

Assignee set to Yukihiro Matsumoto

I must admit having doubts about this proposal being a hoax, but assuming it isn't:

1) This would break a lot of code. As an example, I found 13 instances of `when true/false` in Rails' code that would break.

2) There is no good replacement for the current uses of `when true` and `when false`. In particular, `when true` would basically require separate `if`.

      # From rails/actionpack/lib/action_dispatch/middleware/ssl.rb
      # Current:
      def normalize_hsts_options(options)
        case options
        when false
          # ...
        when nil, true
          # ...
        else
          # ...
        end
      end

      # Ugly rewrite necessary:
      def normalize_hsts_options(options)
        if options == true
          # ...
        else
          case options
          when nil
            # repeated code from `options == true` above...
          when false  # `nil` case must be already taken care of
            # ...
          else
            # ...
          end
      end


3) This makes `when true` almost meaningless and very misleading. `when false` is not useful as it can already be written easily with `when false, nil`

4) Increases the confusion of `true` vs "truthy" and `false` vs "falsey"

5) More importantly, I can not think of a single valid usecase.

`ary.grep(true)` was mentioned. I very much doubt there's much need to do that. We often want to exclude `nil` from a list (that's why we have `compact`), but excluding both `nil` and `false` seem odd, like the values were not computed properly. If there was such a need: `ary.select(&:itself)` works fine and is clear and concise enough.

`ary.grep(false)` seems completely meaningless to me (what can be the use of an array of `nil` and `false` values?) but if it isn't, `ary.reject(&:itself)` works too.

In short, I find the proposal both completely useless and confusing. In case it is somehow deemed necessary, then please define `TRUTHY` and `FALSEY` instead of changing the definitions that have been valid for 20 years.

----------------------------------------
Feature #13067: TrueClass,FalseClass to provide `===` to match truthy/falsy values.
https://bugs.ruby-lang.org/issues/13067#change-62305

* Author: Yukihiro Matsumoto
* Status: Open
* Priority: Normal
* Assignee: Yukihiro Matsumoto
* Target version: 
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I propose to make `TrueClass`, `FalseClass` to provide `===` method to match truthy values (`TrueClass`), and falsy values (`FalseClass`), so that we can use true and false for case pattern matching.  And we can pick truthy values using `grep` e.g. `ary.grep(true)`.

Matz.



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