mqy commented on a change in pull request #9025:
URL: https://github.com/apache/arrow/pull/9025#discussion_r549939736
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File path: rust/arrow/src/datatypes.rs
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@@ -22,6 +22,7 @@
//! * [`Field`](crate::datatypes::Field) to describe one field within a
schema.
//! * [`DataType`](crate::datatypes::DataType) to describe the type of a
field.
+use std::collections::BTreeMap;
Review comment:
Copied from [rust doc
std/collections](https://doc.rust-lang.org/std/collections/index.html):
**`Use a HashMap when:**
You want to associate arbitrary keys with an arbitrary value.
You want a cache.
You want a map, with no extra functionality.
**Use a BTreeMap when:**
You want a map sorted by its keys.
You want to be able to get a range of entries on-demand.
You're interested in what the smallest or largest key-value pair is.
You want to find the largest or smallest key that is smaller or larger than
something.`
The only reason that use `BTreeMap` for `Field` is: don't break the `'Hash`,
`PartialOrd`, `Ord`.
I almost can't image any situation that will sort schemas, unless
compare/sort a schema by versions.
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