[swift-evolution] Revisiting SE-0132 Rationalizing Sequence end-operation names

[Step Christopher]

I second Xiaodi. The new names are much improved. Land them in 4.1 or as soon as possible. Depreciations in 5 and removal in 6, though stability may not allow removal. 

> On Nov 2, 2017, at 9:58 PM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> On Thu, Nov 2, 2017 at 7:26 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
>> 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
> 
> (All of the following IMHO:)
> 
> Swift 4.1 or whatever is closest. The new names are very clear, and their introduction doesn't impair backwards compatibility.
>  
>> And when should we deprecate the old ones?
>> 
>>         1. Swift 4.1
>>         2. Swift 4.n
>>         3. Swift 5
>>         4. Swift 6
>>         5. Never
> 
> Deprecation warnings: Swift 5. Code continues to compile, and fix-its and a migrator can get rid of the warning.
> Removal of deprecated API: Swift 6; ABI stability may require these symbols to continue to exist though.
> 
>> 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.
> 
> Could deprecate in Swift 5--don't feel strongly about this one. Definitely a separate proposal.
>  
>> 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!
>  
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