`Iterator::nth` is badly named

libs
16

To add to the potential churn, there are also nth_back in DoubleEndedIterator (nth_back(0) == last()), as well as slice::select_nth_unstable and its variants.

Some thoughts on why I don't see the naming as a problem:

Method naming uses the natural language meanings, where ordinals start from "first". That is, "first" is an English word for the element before all others in a sequence just like "last" is a word for the one after all others. Adding in "zeroth" as a possibility can only add confusion.

If I see a method named "forty_second", I expect it to return the element at index 41, because in zero-based indexing that is the forty-second element. Similarly, in "nth", the name invokes reference to the ordinal numbers ("first", "second", ...), but as a crucial difference the parameter is taken as a number, where it would be quite surprising to not use zero-based indexing.

One way I can understand nth is that it is mapping the parameter value of type usize to the ordinals, and the zero-based indexing is part of that mapping. In pseudo-code:

fn nth(&mut self, n: usize) -> T {
    const ORDINALS: [fn(&mut Self) -> T] = [first, second, third, ...];
    (ORDINALS[n])(self)
}

To clarify, the only issue I see here is that nth(4) looks like it could mean fourth(), but one already has to read v[4] as the fifth element.

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