on Tue Apr 12 2016, Jonathan Hull <swift-evolution@swift.org> wrote:
> I would really like to see something like the following added to the standard
> library:
>
> extension Dictionary {
>
> func mapValues<U>(transform:(Key,Value)->U)->[Key:U] {
> var output:[Key:U] = [:]
> for (k,v) in self {
> output[k] = transform(k,v)
> }
> return output
> }
>
> }
>
> It comes up enough that I have had to add it to pretty much every one of my
> projects. I also don’t feel comfortable adding it to my frameworks, since I
> figure a lot of people are also adding something like this to their projects,
> and I don’t want to cause a conflict with their version. Prime candidate for
> the
> standard library.
>
> I like calling it ‘mapValues' as opposed to providing an override for map,
> since
> it makes the specific behavior more clear. I would expect ‘map' to possibly
> map
> the keys as well (though there are issues where the new keys overlap). I
> suppose
> you could just have a bunch of overrides for map if the compiler becomes good
> enough at differentiating return types: (Value)->(Value), (Key,Value)->Value,
> (Key, Value)->(Key,Value)
I agree that we need a way to do this, and was surprised when what I
tried didn't work. This should work:
Dictionary(d.lazy.map { (k, v) in (k, transform(v)) })
We should have a proposal that makes the constructor work* if we don't
already have one.
I'm inclined against building specialized variants of basic algorithms
into particular collections, though. Could be talked out of it if the
use-case is strong enough.
------
* Only question: does this need a label, e.g.
Dictionary(uniquingKeys: d.lazy.map { (k, v) in (k, transform(v)) })
to denote that it's lossy?
--
Dave
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