[swift-evolution] Revisiting SE-0110

[Dave Abrahams]

on Sun May 28 2017, Gwendal Roué <gwendal.roue-AT-gmail.com> wrote:

>> Le 27 mai 2017 à 19:43, Dave Abrahams via swift-evolution <swift-evolution at swift.org> a écrit :
>> 
>> 
>> on Thu May 25 2017, Gwendal Roué <swift-evolution at swift.org <mailto:swift-evolution at swift.org>>
> wrote:
>> 
>
>>>> Furthermore, this probably comes up most commonly with dictionaries,
>>>> since they're a sequence of tuples. The element tuple for
>>>> dictionaries has element labels (key: Key, value: Value), so instead
>>>> of writing `{ tuple in let (key, value) = tuple; f(key, value) }`,
>>>> you could use the implicit argument and write `{ f($0.key, $0.value)
>>>> }`.
>>>> 
>>>> -Joe
>>> 
>>> I've migrated a project from Swift 3 to Swift 4 (relevant commit:
>>> https://github.com/groue/GRDB.swift/commit/4f26cbcacf7b783c9c503f2909f2eb03ef7930fe)
>>> 
>>> Joe is right, dictionaries, as handy as they are, are particularly affected. But $0 is hardly a
>>> panacea.
>>> 
>>> What I regret the most with the change is the lost ability to give
>>> *relevant names* to tuple elements (and sometimes with the forced
>>> introduction of a phony variable that has no relevant name (like
>>> "pair").
>> 
>> Not saying there's no problem here, but `kv` (or `keyValue` if you must)
>> works pretty well for this.  At least it isn't purely a reflection of
>> the type and gives some hint as to semantics.
>
> Let me please try to be understood:
>
> A dictionary is a convenience type, with many many purposes. One
> rarely thinks of a dictionary as a "dictionary". It's more often a
> "cache", or a "name1 to name2 mapping", as in "name to position
> mapping", "lowercase string to case-preserved string mapping", or
> whatever you want.
>
> The "kv", "pair", "key", "value" identifiers are not only irrelevant,
> they actively hinder code readability. Compare:
>
> - ...map { $0.key ... $0.value ... }
> - ...map { (name, position) in name ... position ... }

I agree with you.  As I said, I'm not trying to say there's no problem
here.  

-- 
-Dave