[swift-evolution] rename dropFirst() and dropLast()

[Daniel Duan]

For concrete types that conform to CollectionType:

[2, 1, 3].removeFirst()    // => 2
[2, 1, 3].removingFirst() // => [1, 3]

seems like what the “non-mutating counterpart” guideline is aiming for. As another example, the guideline includes “stripNewlines()” and “strippingNewlines()”.

For SequenceType conforming types that aren’t CollectionTypes, they would be stuck with “removingFirst()”, which, technically, is a noun phrase (again, not my personal favorite). I don’t this result is against anything in the guidelines.



> On Dec 29, 2015, at 12:43 PM, Kevin Ballard <kevin at sb.org> wrote:
> 
> Actually that's not true, CollectionType does not define dropFirst(). It merely provides a default implementation. dropFirst() is only actually defined in SequenceType, which does not have any mutating methods. Renaming it to "removingFirst()" would be against the guidelines for all sequences that are not also RangeReplaceableCollectionTypes.
> 
> -Kevin Ballard
> 
> On Tue, Dec 29, 2015, at 12:39 PM, Daniel Duan wrote:
>> I made the same observation on Haskell in the original post :)
>> 
>> “removeFirst()” is also defined in CollectionType. So “dropFirst()” is removeFirst()’s – in the Guidelines’ term – "non-mutating counterpart" for all CollectionTypes. Therefore, “removingFirst()” would be the winner.
>> 
>> (My personal preference notwithstanding, that is).
>> 
>>> On Dec 29, 2015, at 12:15 PM, Kevin Ballard <kevin at sb.org> wrote:
>>> 
>>> I guess that's a good argument for keeping "prefix" and "suffix" instead of "take" and "takeEnd". But there is no good noun phrase to use for dropFirst/dropLast (Haskell's "init" and "tail" are nouns but they're very confusing and don't really make sense once you add in an integral argument anyway). The guidelines do say it's acceptable to use an imperative verb if there is no good noun phrase, so "skip" and "skipEnd" (or "skipLast", or maybe "skipSuffix" if we're keeping "suffix") are still reasonable.
>>> 
>>> Incidentally, it occurs to me that "removingFirst" is actually not an appropriate name here, because dropFirst is a method of SequenceType, and SequenceType does not have mutating methods. removeFirst is actually defined by RangeReplaceableCollectionType (and by Set, and also by CollectionType if SubSequence == Self).
>>> 
>>> -Kevin Ballard
>>> 
>>> On Tue, Dec 29, 2015, at 11:55 AM, Daniel Duan wrote:
>>>> Hi Kevin,
>>>> 
>>>> “take" and “skip” are fine as free function names. As method names, they are a step back from following the API Guidelines (“non-mutating methods should read as noun phrases”).
>>>> 
>>>> - Daniel
>>>> 
>>>>> On Dec 29, 2015, at 11:40 AM, Kevin Ballard via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> 
>>>>> On Mon, Dec 28, 2015, at 04:23 PM, Kevin Ballard wrote:
>>>>>> That said, `droppingFirst` sounds pretty weird to me. "drop" (and the related verb "take" that we're not using) has precedent in multiple languages (Rust and Haskell come to mind) to mean "return a new sequence that skips the first N elements". And I'm not aware of any language that sets precedent for the verb "drop" to mean "mutate the receiver".
>>>>> 
>>>>> Hmm, I just took a look, and while Rust does use "take", it actually doesn't use "drop" (but Haskell does). Instead it uses "skip", which seems like a good candidate if we're going to rename this. I'm tempted to say we should use "take" instead of "prefix" as well, because `seq.prefix(3)` isn't actually immediately obvious what it does (as the verb "prefix" usually means to add onto the front, not to take the front). And we can use "takeLast" for "suffix" (neither Rust nor Haskell appears to have an equivalent of takeLast; I believe Rust doesn't because none of its iterator adaptors use dynamically-allocated memory, and I think Haskell expects you to just do `reverse . take n . reverse`). Although I do notice Haskell has a function dropWhileEnd that drops the suffix, which suggests "takeEnd" and "dropEnd" here.
>>>>> 
>>>>> Which is to say, if we're going to rename these methods, my vote is:
>>>>> 
>>>>> prefix -> take
>>>>> suffix -> takeEnd or takeLast
>>>>> dropFirst -> skip
>>>>> dropLast -> skipEnd or skipLast
>>>>> 
>>>>> -Kevin Ballard
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>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>> 
>>