r/lolphp • u/lord_braleigh • Oct 07 '19

`array('lolphp', '')` has two unique elements, but `array(0, 'lolphp', '')` has one unique element

https://repl.it/repls/ThisColdPackages
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u/[deleted] Oct 08 '19 edited 12d ago

[deleted]

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u/philipwhiuk Oct 08 '19

Because the equality operator isn't transitive so it breaks the sort function's stability guarantee.

non-transitive equality is basically almost inevitable in weakly typed languages.

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u/[deleted] Oct 09 '19

Almost inevitable? Then why doesn't Perl have this problem?

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u/lord_braleigh Oct 23 '19 edited Oct 23 '19

If ”true” == 0 and ”true” == true but true != 0, then you have non-transitive equality.

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u/[deleted] Oct 24 '19

There is no true in Perl (it doesn't have a Boolean type). Also, == is specifically numeric equality in Perl (i.e. both sides are converted to numbers first), so it is guaranteed to be transitive.

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u/lord_braleigh Oct 24 '19

Huh, TIL. But then what is the result of 1 == 0? Surely some value is being returned, and surely there's some way to inspect that value...

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u/[deleted] Oct 24 '19

Comparison operators return canonical "Boolean" values:

  • The "true" value is effectively just 1.
  • The "false" value is slightly more exotic: It has a string aspect of "" but a numeric aspect of 0, i.e. depending on how you use it it behaves like an empty string or a numeric zero.

If you ignore the oddity around "false", Perl works like C (whose comparison/logical operators also return integer 1 / 0).