RFC 0580: rename-collections

libs (collections | convention)

• Start Date: 2015-01-13
• RFC PR: rust-lang/rfcs#580
• Rust Issue: rust-lang/rust#22479

Summary

Rename (maybe one of) the standard collections, so as to make the names more consistent. Currently, among all the alternatives, renaming BinaryHeap to BinHeap is the slightly preferred solution.

Motivation

In this comment in the Rust 1.0.0-alpha announcement thread in /r/programming, it was pointed out that Rust's std collections had inconsistent names. Particularly, the abbreviation rules of the names seemed unclear.

The current collection names (and their longer versions) are:

• Vec -> Vector
• BTreeMap
• BTreeSet
• BinaryHeap
• Bitv -> BitVec -> BitVector
• BitvSet -> BitVecSet -> BitVectorSet
• DList -> DoublyLinkedList
• HashMap
• HashSet
• RingBuf -> RingBuffer
• VecMap -> VectorMap

The abbreviation rules do seem unclear. Sometimes the first word is abbreviated, sometimes the last. However there are also cases where the names are not abbreviated. Bitv, BitvSet and DList seem strange on first glance. Such inconsistencies are undesirable, as Rust should not give an impression as "the promising language that has strangely inconsistent naming conventions for its standard collections".

Also, it should be noted that traditionally ring buffers have fixed sizes, but Rust's RingBuf does not. So it is preferable to rename it to something clearer, in order to avoid incorrect assumptions and surprises.

Detailed design

First some general naming rules should be established.

1. At least maintain module level consistency when abbreviations are concerned.
2. Prefer commonly used abbreviations.
3. When in doubt, prefer full names to abbreviated ones.
4. Don't be dogmatic.

And the new names:

• Vec
• BTreeMap
• BTreeSet
• BinaryHeap
• Bitv -> BitVec
• BitvSet -> BitSet
• DList -> LinkedList
• HashMap
• HashSet
• RingBuf -> VecDeque
• VecMap

The following changes should be made:

• Rename Bitv, BitvSet, DList and RingBuf. Change affected codes accordingly.
• If necessary, redefine the original names as aliases of the new names, and mark them as deprecated. After a transition period, remove the original names completely.

Why prefer full names when in doubt?

The naming rules should apply not only to standard collections, but also to other codes. It is (comparatively) easier to maintain a higher level of naming consistency by preferring full names to abbreviated ones when in doubt. Because given a full name, there are possibly many abbreviated forms to choose from. Which one should be chosen and why? It is hard to write down guidelines for that.

For example, the name BinaryBuffer has at least three convincing abbreviated forms: BinBuffer/BinaryBuf/BinBuf. Which one would be the most preferred? Hard to say. But it is clear that the full name BinaryBuffer is not a bad name.

However, if there is a convincing reason, one should not hesitate using abbreviated names. A series of names like BinBuffer/OctBuffer/HexBuffer is very natural. Also, few would think that AtomicallyReferenceCounted, the full name of Arc, is a good type name.

Advantages of the new names:

• Vec: The name of the most frequently used Rust collection is left unchanged (and by extension VecMap), so the scope of the changes are greatly reduced. Vec is an exception to the "prefer full names" rule because it is the collection in Rust.
• BitVec: Bitv is a very unusual abbreviation of BitVector, but BitVec is a good one given Vector is shortened to Vec.
• BitSet: Technically, BitSet is a synonym of BitVec(tor), but it has Set in its name and can be interpreted as a set-like "view" into the underlying bit array/vector, so BitSet is a good name. No need to have an additional v.
• LinkedList: DList doesn't say much about what it actually is. LinkedList is not too long (like DoublyLinkedList) and it being a doubly-linked list follows Java/C#'s traditions.
• VecDeque: This name exposes some implementation details and signifies its "interface" just like HashSet, and it doesn't have the "fixed-size" connotation that RingBuf has. Also, Deque is commonly preferred to DoubleEndedQueue, it is clear that the former should be chosen.

Drawbacks

• There will be breaking changes to standard collections that are already marked stable.

Alternatives

A. Keep the status quo:

And Rust's standard collections will have some strange names and no consistent naming rules.

B. Also rename Vec to Vector:

And by extension, Bitv to BitVector and VecMap to VectorMap.

This means breaking changes at a larger scale. Given that Vec is the collection of Rust, we can have an exception here.

C. Rename DList to DLinkedList, not LinkedList:

It is clearer, but also inconsistent with the other names by having a single-lettered abbreviation of Doubly. As Java/C# also have doubly-linked LinkedList, it is not necessary to use the additional D.

D. Also rename BinaryHeap to BinHeap.

BinHeap can also mean BinomialHeap, so BinaryHeap is the better name here.

E. Rename RingBuf to RingBuffer, or do not rename RingBuf at all.

Doing so would fail to stop people from making the incorrect assumption that Rust's RingBufs have fixed sizes.

Unresolved questions

None.