Commits on Dec 10, 2020

1. Add some core::cmp::Ordering helpers …

   ...to allow easier greater-than-or-equal-to and less-than-or-equal-to
   comparisons, and variant checking without needing to import the enum,
   similar to `Option::is_none()` / `Option::is_some()`, in situations where
   you are dealing with an `Ordering` value. (Simple `PartialOrd` / `Ord`
   based evaluation may not be suitable for all situations).
   
   Prior to Rust 1.42 a greater-than-or-equal-to comparison might be written
   either as a match block, or a traditional conditional check like this:
   
   ```rust
   if cmp == Ordering::Equal || cmp == Ordering::Greater {
       // Do something
   }
   ```
   
   Which requires two instances of `cmp`. Don't forget that while `cmp` here
   is very short, it could be something much longer in real use cases.
   
   From Rust 1.42 a nicer alternative is possible:
   
   ```rust
   if matches!(cmp, Ordering::Equal | Ordering::Greater) {
       // Do something
   }
   ```
   
   The commit adds another alternative which may be even better in some cases:
   
   ```rust
   if cmp.is_ge() {
       // Do something
   }
   ```
   
   The earlier examples could be cleaner than they are if the variants of
   `Ordering` are imported such that `Equal`, `Greater` and `Less` can be
   referred to directly, but not everyone will want to do that.
   
   The new solution can shorten lines, help avoid logic mistakes, and avoids
   having to import `Ordering` / `Ordering::*`.

   

   jnqnfe committed Dec 10, 2020
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