No definition of lexicographic order in docs for `Iterator::cmp*`

[brmmm3]

It seems that the comparison functions are not correctly implemented.

I tried this code:

use std::cmp::Ordering;

assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::Less);
assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::Greater);

I expected to see this happen:
The code above should panic. The reason is: 1 is NOT less than 1 and 1 is NOT greater than 1.
What I'm missing in Ordering are LessOrEqual and GreaterOrEqual. If these 2 objects would exist I could write:

use std::cmp::Ordering;

assert_eq!([1].iter().cmp([1, 2].iter()), Ordering::LessOrEqual);
assert_eq!([1, 2].iter().cmp([1].iter()), Ordering::GreaterOrEqual);

which would correct not panic.

Meta

I've tried this in Rust Playground with stable and nightly.

[ecstatic-morse]

Quoting the docs for the C++ standard library (emphasis mine):

Lexicographical comparison is a operation with the following properties:

• Two ranges are compared element by element.
• The first mismatching element defines which range is lexicographically less or greater than the other.
• If one range is a prefix of another, the shorter range is lexicographically less than the other.
• If two ranges have equivalent elements and are of the same length, then the ranges are lexicographically equal.
• An empty range is lexicographically less than any non-empty range.
• Two empty ranges are lexicographically equal.

Iterator::cmp performs a lexicographical comparison. We should probably define lexicographical order wherever the term is used in the standard library documentation.

[ecstatic-morse]

To resolve this, you can either write a definition of lexicographical order somewhere in the rust documentation or link to an easily understandable source. Then link to that definition wherever "lexicographical" appears in the source. FWIW, I don't think the wikipedia article qualifies as "easily understandable".

[softwaredeveloptam]

Hi I would like to take this on as a first issue if that's okay.
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[Alexendoo]

Triage: Hi, are you still working on this issue @softwaredeveloptam?

[softwaredeveloptam]

Hey there, @Alexendoo I got pretty busy and it slipped my mind, but will give it a shot this week!

[Rustin170506]

I am working on this.
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