> Le 24 janv. 2017 à 04:31, Brent Royal-Gordon via swift-evolution
> <[email protected]> a écrit :
>
>>> The operands and sense of the comparison are kind of lost in all this
>>> garbage. You really want to see `foo < bar` in this code somewhere, but you
>>> don't.
>>
>> Yeah, we thought about trying to build a DSL for that, but failed. I think
>> the best possible option would be something like:
>>
>> foo.comparison(case: .insensitive, locale: .current) < bar
>>
>> The biggest problem is that you can build things like
>>
>> fu = foo.comparison(case: .insensitive, locale: .current)
>> br = bar.comparison(case: .sensitive)
>> fu < br // what does this mean?
>>
>> We could even prevent such nonsense from compiling, but the cost in library
>> API surface area is quite large.
>
> Is it? I think we're talking, for each category of operation that can be
> localized like this:
>
> * One type to carry an operand and its options.
> * One method to construct this type.
> * One alternate version of each operator which accepts an operand+options
> parameter. (I'm thinking it should always be the right-hand side, so the long
> stuff ends up at the end; Larry Wall noted this follows an "end-weight
> principle" in natural languages.)
>
> I suspect that most solutions will at least require some sort of overload on
> the comparison operators, so this may be as parsimonious as we can get.
SQL has the `collate` keyword:
-- sort users by email, case insensitive
select * from users order by email collate nocase
-- look for a specific email, in a case insensitive way
select * from users where email = '[email protected]
<mailto:[email protected]>' collate nocase
It is used as a decorator that modifies an existing sql snippet (a sort
descriptor first, and a comparison last)
When designing an SQL building to Swift, I chose the
`nameColumn.collating(.nocase)` approach, because it allowed a common Swift
syntax for both use cases:
// sort users by email, case insensitive
User.order(nameColumn.collating(.nocase))
// look for a specific email, in a case insensitive way
User.filter(nameColumn.collating(.nocase) == "[email protected]
<mailto:[email protected]>")
Yes, it comes with extra operators so that nonsensical comparison are avoided.
But it just works.
Gwendal
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