> I'm trying to think of a case where you'd want a custom implementation of ne... I'm not sure I can come up with one One old example from school was comparing

> I'm trying to think of a case where you'd want a custom implementation of ne... I'm not sure I can come up with one One old example from school was comparing unordered sets of numbers, each backed by a flat array. Summing such an array, contiguous in memory, was very fast: faster than many individual numeric comparisons. So "not equals" checked for equal sums before dropping back to iteration. Of course, that only made sense in situations where more things weren't equal (and didn't share sums) than not, but it helped someone win some performance/vanity extra credit. And I didn't know about vectorized code at the time, so that might make it a wash. A similar example might be with probablistic checksums of large data. If a checksum answers "maybe the same or definitely not the same" a la a HyperLogLog, comparing checksums is a quick way out for "not equals". Of course, that'd require some uniquely small/untrustworthy checksums, or some uniquely paranoid comparison programmers! That applies similarly to "equals", though. About the only even vaguely realistic example I can think of is for non-complementary notions of equality and inequality, i.e. an application context in which case it makes sense to have rules like "two MyLists are equal if they contain the same elements, but are not equal if they contain different elements or have different orders". And I call that "realistic" because I've seen code do things like that .... not because it's anything but a terrible idea.