[ruby-core:91926] [Ruby trunk Feature#15722] `Kernel#case?`

Issue #15722 has been updated by osyo (manga osyo).


How about `Enumerable#case?` ? 
Comparing with `===` like `Enumerable#include?`.

```ruby
bar # => "bar"
["foo", "bar", "baz"].case? bar # => true
["qux"].case? bar               # => false
[Symbol, String].case? bar      # => true
[Array].case? bar               # => false
```


----------------------------------------
Feature #15722: `Kernel#case?`
https://bugs.ruby-lang.org/issues/15722#change-77258

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
I often want to use `===` to match a single object on the right side against multiple objects on the left, as is used in `case`-constructions, just to return a truth value, and end up writing like this:

```ruby
bar # => "bar"
flag1 = case bar; when "foo", "bar", "baz"; true; end # => true
flag2 = case bar; when Symbol, String; true; end # => true
```

I propose `Kernel#case?` that should work like this:

```ruby
bar # => "bar"
bar.case?("foo", "bar", "baz") # => true
bar.case?("qux") # => false
bar.case?(Symbol, String) # => true
bar.case?(Array) # => false
bar.case? # => false
```

It is similar to Rails' `in?`, but it differs from it in that it uses `===` for comparison, not `==`.



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