> Le 9 janv. 2018 à 17:16, Zach Waldowski via swift-evolution
> <swift-evolution@swift.org> a écrit :
>
> I'm not sure a valid use case by a third party makes it hold its weight for
> inclusion in the stdlib.
You're definitely right, and that's why I wrote with the most humble tone I
could.
Yet, the design of the stdlib *requires* some speculation about use cases, and
speculation is *helped* by the exposition of actual uses. I'm not sure readers
of the mailing list had any idea of the use cases of the current
DictionaryLiteral, and maybe I helped a little.
> Reproducing its feature set is extremely trivial, and would probably allow
> you to hint the implementation details better for your use case.
Please define "trivial".
In case anybody would wonder, in the line below the `row` variable is of type
Row which happens to adopt ExpressibleByDictionaryLiteral. It is not of type
DictionaryLiteral. The use case here is the ability to express a row with a
dictionary literal that accepts duplicated keys and preserves ordering:
XCTAssertEqual(row, ["a": 1, "a": 2])
I don't see how anything could better fit this use case than the current
DictionaryLiteral. This is not *my* use case, but the use case of anyone that
wants to model database rows beyond the traditional (and ill-advised)
dictionary.
Some other users may come with other use cases that may also help the stdlib
designers choose the best solution.
Gwendal
>
> Zach
> z...@waldowski.me <mailto:z...@waldowski.me>
>
>
> On Tue, Jan 9, 2018, at 2:12 AM, Gwendal Roué via swift-evolution wrote:
>>
>>> Le 9 janv. 2018 à 08:06, Gwendal Roué via swift-evolution
>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> a écrit :
>>>
>>>
>>>> Le 9 janv. 2018 à 06:40, Nevin Brackett-Rozinsky via swift-evolution
>>>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> a écrit :
>>>>
>>>> The ulterior question of whether preserving “DictionaryLiteral” is
>>>> worthwhile, is apparently out of scope. Personally, I have a hard time
>>>> imagining a compelling use-case outside of the standard library, and I
>>>> doubt it’s being used “in the wild” (I checked several projects in the
>>>> source-compatibility suite and found zero occurrences).
>>>
>>> DictionaryLiteral is worthwhile. The SQLite library GRDB uses
>>> DictionaryLiteral in order to build database rows (which may have
>>> duplicated column names, and whose column ordering is important). This is
>>> mostly useful for tests:
>>>
>>> let row = try Row.fetchOne(db, "SELECT 1 AS a, 2 AS a")!
>>> XCTAssertEqual(row, ["a": 1, "a": 2])
>>>
>>> Gwendal
>>
>> Chris Lattner's wrote:
>>
>>> why is maintaining duplicate keys a feature?
>>
>>> Since it is immutable, why not sort the keys in the initializer, allowing
>>> an efficient binary search to look up values?
>>
>>
>> I really wish both duplicated keys and key ordering would be preserved,
>> since both are needed for the above sample code.
>>
>> Should those features be lost, the sky wouldn't fall, that's sure. But we'd
>> have to write something much less easy to wrote and read:
>>
>> XCTAssertEqual(row.map { $0 }, [("a", 1), ("a", 2)])
>>
>> Gwendal
>>
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