Issue #15857 has been updated by shuujii (Shuji KOBAYASHI).


@jeremyevans0 Thank you for your comment. About `Complex`, I agree with most of v2 patch, but I have some comments.

- Should methods from `Comparable` that are currently disabled be enabled?
- `rb_undef_method(rb_cComplex, "<=>")` is unneeded.
- `idCmp` can be used instead of `id_spaceship`.

About other than `Complex`, `<=>` of some classes, such as `String` and `Time`, will fail if LHS does not implement `<=>`. It's better to return `nil` in this case too, because whether it's comparable or not and whether LHS implements `<=>` or not is essentially irrelevant, I think.

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Bug #15857: <=> の右辺が <=> を実装していない場合の振る舞い
https://bugs.ruby-lang.org/issues/15857#change-78437

* Author: shuujii (Shuji KOBAYASHI)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
`<=>` の右辺が `<=>` を実装していないとき、`nil` が返却される場合と例外が発生する場合があり一貫性がないように思えるのですが、意図的でしょうか。

```ruby
  0 <=> 0i               #=> NoMethodError (undefined method `<=>' for (0+0i):Complex)
  0 <=> BasicObject.new  #=> nil
 :a <=> 0i               #=> nil
"a" <=> 0i               #=> NoMethodError (undefined method `<=>' for (0+0i):Complex)

```

なお、`0 <=> 0i` に関しては、`0 == 0i` は `true` になるのでそれとも一貫性がないように思えるのもやや気になりました。

---Files--------------------------------
complex-real-spaceship.patch (8.75 KB)
complex-real-spaceship-v2.patch (8.08 KB)


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