During the Swift 3 cycle, I proposed SE-0132, "Rationalizing Sequence
end-operation names". It was rejected because it needed revision and there was
no time to do so. Since then, part of the proposal—partial ranges and the
`RangeExpression` slicing protocol—has been adopted in SE-0172, "One-sided
Ranges". I''d like to reopen discussion of the rest of the proposal.
To refresh your memory, SE-0132 proposed systematically renaming a number of
`Sequence` and `Collection` methods which operate on the beginning and end of a
sequence. Many of these methods have names borrowed directly from functional
programming; they use terminology in conflicting ways and don't follow our
conventions for non-mutating method names. For example, consider the
inconsistent and API Guideline-violating names of a few members which operate
on the beginning of a sequence or collection:
first dropFirst() removeFirst()
prefix(_:) dropFirst(_:) removeFirst(_:)
prefix(while:) drop(while:) —
These members could be renamed to form consistent "families" where a given term
always meant the same thing:
first removingFirst() removeFirst()
prefix(_:) removingPrefix(_:) removePrefix(_:)
prefix(while:) removingPrefix(while:) —
The main question in my mind about this plan is source stability. Back during
Swift 3, we broke compatibility willy-nilly, but today we're being a little
more circumspect. I believe these names meet the criteria of being actively
harmful—they are difficult to discover, so developers don't use these members
even when they should, and many of them sound like mutating methods or are
unclear about their purpose—but that still doesn't tell us how we should treat
the old names.
Basically, when should we introduce the new names?
1. Swift 4.1 (or whatever pre-Swift 5 version the proposal ends up
landing in)
2. Swift 4.n (the version of Swift 5's compatibility mode for Swift 4)
3. Swift 5
And when should we deprecate the old ones?
1. Swift 4.1
2. Swift 4.n
3. Swift 5
4. Swift 6
5. Never
I'm also open to discussion about whether this should be done at all, whether
any additional methods should be included (or included methods should be left
alone), whether the now-obsolete `prefix(from:)` `prefix(upTo:)`, and
`prefix(through:)` methods should be left alone, deprecated, or removed, and
whether this should be done in this proposal or a different one.
The original proposal, which lists all affected methods and explains the logic
behind them, is available at
<https://github.com/apple/swift-evolution/blob/master/proposals/0132-sequence-end-ops.md>.
Keep in mind that the parts about ranges have already been incorporated into
Swift in a revised form, so you can ignore them.
I'll get cracking on an implementation once we figure out what I should
implement.
Thanks!
--
Brent Royal-Gordon
Architechies
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