min_by requires Ord not PartialOrd

[steveklabnik]

Issue by neunenak
Tuesday Sep 30, 2014 at 06:15 GMT

For earlier discussion, see rust-lang/rust#17648

This issue was labelled with: A-iterators, A-libs, B-RFC in the Rust repository

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It would be handy if Iterator::min_by required PartialOrd instead of Ord. This requirement makes it impossible to use with among other common types f32 and f64, which is annoying. I don't know if the best solution is to simply change the required trait to PartialOrd or to provide some other method min_by_partial_ord or something along those lines. The same reasoning should apply to Iterator::max_by

[jimblandy]

Possible revisions to max_by and min_by that would make this problem go away are being discussed in Rust issue 15311. Summary: "scoring" functions like the one expected by max_by have disadvantages; expecting a function that does the comparison and returns a bool or Ordering might work better.

[Centril]

I believe this is non-actionable now; and there's https://doc.rust-lang.org/nightly/std/iter/trait.Iterator.html#method.min_by which doesn't require any T: Ord.