JavaScript: The Curious Case of null &gt;= 0

Re:JavaScript: The Curious Case of null >= 0 by mrgriffin on Saturday September 09, 2017 @10:18AM (#15207187)

I find this behavior surprising:

  >>> d = {0: "int"}
  >>> d[False] = "bool"
  >>> d
  {0: 'bool'}
  >>> nan = float('nan')
  >>> d[nan] = 0
  >>> d[nan] = 1
  >>> d
  {0: 'bool', nan: 0, nan: 1}

Yes, yes, it's because issubclass(bool, int) == True, and nan != nan, but weird.

And if we include Python 2 you get the truly ridiculous:

  >>> dict() < set()
  True
  >>> dict < set()
  False
  >>> 0 < dict
  True
  >>> 0 < 1j
  TypeError: no ordering relation is defined for complex numbers

To compare e.g. a dictionary and set we compare the _names_ of the types! Except complex numbers, because they don't have an ordering. I actually have come across this as a bug in production.

Personally I'd just make any comparison involving different types an error. That probably interacts poorly with subtyping, but it's a price I'm willing to pay.

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Re:JavaScript: The Curious Case of null >= 0 by guitarbill on Saturday September 09, 2017 @10:50AM (#15207334)

The `nan` thing is actually because `float('nan')` can (and does) return a new object (well, with a different ID) each time. So it's like going `d[object()] = 'a'; d[object()] = 'b'` and not retaining the objects for lookup.

> Personally I'd just make any comparison involving different types an error

As you point out, this is what Python 3 did for `None`. But it's been idiomatic to have 0 = False when languages didn't have `False`; so `bool(0) == False` makes sense, but also `sum(boolean for boolean in sequence)` works. So you could argue that for `True` and `False`, meaningful coercion is possible, and in reverse, if zero is false-y and everything else is truth-y (like in C), then that also makes sense. Imagine if you had to cast every number to a boolean explicitly! So I guess having `d[0] == d[False]` is the lesser of evils.

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Re:JavaScript: The Curious Case of null >= 0 by moomin on Saturday September 09, 2017 @11:33AM (#15207553)

My favourite of these is Haskell

> "" = [] True

Which makes perfect sense if you know any Haskell, but looks like a JavaScript wat if you don't.

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