Issue #17857 has been updated by jeremyevans0 (Jeremy Evans).


I've submitted a pull request to fix this: https://github.com/ruby/ruby/pull/4496

----------------------------------------
Bug #17857: `when 0r` and `when 0i` do not match with `case 0`
https://bugs.ruby-lang.org/issues/17857#change-91923

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
The following code prints `:bar` between Ruby 2.1 .. 2.5, and dumps core since Ruby 2.6.

```
case 0
when 0r
  p :foo
else
  p :bar #=> :bar
end
```

A Complex has the same issue.

```
case 0
when 0i
  p :foo
else
  p :bar #=> :bar
end
```

The segfault issue was fixed by #17854. So the current master it prints `:bar`.

However, I believe it should print `:foo` because `0r === 0` evaluates to true. This weird behavior is caused by the optimization which uses a hidden hash to dispatch to when clauses. By disabling the optimization, the code prints `:foo`.

```
opt = RubyVM::InstructionSequence.compile_option
opt[:specialized_instruction] = false
RubyVM::InstructionSequence.compile(<<END, **opt).eval
case 0
when 0r
  p :foo #=> :foo
else
  p :bar
end
END
```

I think the optimization should be disabled when T_RATIONAL or T_COMPLEX are used.



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