[swift-evolution] [Discussion] Sortable Attribute

[Shawn Erickson]

I think a first class sort descriptor style would robustly solve most
complex sorting needs. It can deal with multiple sort dimensions, etc.
which an attribute wouldn't really solve without language complexity.

On Wed, Aug 17, 2016 at 1:12 AM David Rönnqvist <swift-evolution at swift.org>
wrote:

> Haskell also has a `comparing` function
>
>     comparing :: (Ord a) => (b -> a) -> b -> b -> Ordering
>
> which applies a function on both the left hand side and the right hand
> side to get two values that can be compared/ordered.
> This makes the call site look something like this:
>
>     sortBy (comparing length) names
>
> The same *can* be done in Swift, resulting in a similar and very
> English-like calls site:
>
>     names.sort(by: comparing { $0.characters.count })
>
> That said. While this (the `comparing` function) is a fun exercise in
> higher order functions, a more Swifty syntax for this is probably a
> separate overload of the sort/ed/ function.
>
> - David
>
> On 17 Aug 2016, at 02:17, Silvan Mosberger via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I'd be in favor. We'd need another name, since the current closure
> predicate is already standardized to `by:`.
>
>
> Haskell uses "on" for sorting with a mapping. There are both
>
> sortOn :: Ord
> <http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Ord.html#t:Ord> b
> => (a -> b) -> [a] -> [a]
>
> and
>
> sortBy :: (a -> a -> Ordering
> <http://hackage.haskell.org/package/base-4.9.0.0/docs/Data-Ord.html#t:Ordering>)
> -> [a] -> [a]
>
> in Haskell.
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