> From: Dave Abrahams <[email protected]>
> To: Brent Royal-Gordon <[email protected]>
>
>> While it's great that `compared(to:case:etc.)` is parallel to
>> `compared(to:)`, you don't actually want to *use* anything like
>> `compared(to:)` if you can help it. Think about the clarity at the use site:
>>
>> if foo.compared(to: bar, case: .insensitive, locale: .current) == .before
>> { … }
>
> Right. We intend to keep the usual comparison operators.
>
> Poor readability of "foo <=> bar == .before" is another reason we think that
> giving up on "<=>" is no great loss.
>
>> 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.
>
>> I'm struggling a little with the naming and syntax, but as a general
>> approach, I think we want people to use something more like this:
>>
>> if StringOptions(case: .insensitive, locale: .current).compare(foo < bar)
>> { … }
>
> Yeah, we can't do that without making
>
> let a = foo < bar
>
> ambiguous
So, cue crazy idea #1, but what about something like this?
struct StringComparison {
let leftHand: String
let rightHand: String
let comparison: SortOrder
var insensitive: Bool {
...
}
// … etc
}
func <(lhs: String, rhs: String) -> StringComparison { // similar for ==, >,
etc.
return StringComparison(leftHand: lhs, rightHand: rhs, comparison:
.before)
}
Then:
if (a < b).insensitive {
...
}
This would fix the ambiguity of:
let a = foo < bar // ‘a' is StringComparison
if a.insensitive {
}
IMHO, the big problem with this is that the most obvious default case really
should fall-through to a boolean value for the comparison struct:
if a < b { // case-sensitive, non-localized compare
...
}
...but I can’t figure out how to make that work without the old BooleanType
protocol, maybe someone smarter than I could…
—Karim
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