[ruby-core:83615] [Ruby trunk Bug#1720] [NaN] == [NaN] が true になる

Issue #1720 has been updated by Eregon (Benoit Daloze).


Could someone summarize in English the rationale?

~~~ ruby
Float::NAN == Float::NAN # => false
~~~

The documentation says:

~~~
The result of NaN == NaN is undefined, so the implementation-dependent
value is returned.
~~~

But this is true no matter the environment, isn't it? (NaN is the only numeric value never equal to itself)

And then we have:

~~~ ruby
[Float::NAN] == [Float::NAN] # => true
[0.0/0] == [Float::NAN] # => false
~~~

Which sounds to me like a bad side effect of short-circuiting in rb_equal on

~~~ c
if (a == b)
    return Qtrue;
else
    return rb_funcall(a, "==", 1, b);
~~~

----------------------------------------
Bug #1720: [NaN] == [NaN] が true になる
https://bugs.ruby-lang.org/issues/1720#change-67636

* Author: tadf (tadayoshi funaba)
* Status: Closed
* Priority: Normal
* Assignee: mrkn (Kenta Murata)
* Target version: 2.0.0
* ruby -v: ruby 1.9.2dev (2009-07-03 trunk 23945) [i686-linux]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
=begin
 NaN = 0.0/0
 [NaN] == [NaN] が true になりますが、
 
 NaN == NaN #=> false
 [1] == [1.0] #=> true
 
 という結果からするとおかしいように思います。
=end




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