CODEWITHSUNDEEP
higher-order-functionsswift5
Fattie
Fattie

Reputation: 12687

Latest Swift, compact map by case?

I'm doing this,

let x = results.compactMap {
    if case .person (let P) = $0 { return P }
    else { return nil }
}

x is [Person] , obviously results is something like

enum ResultItem: Decodable {
    case person(Person)
    case cat(Cat)
    case budgie(Budgie)

Anyway I'm doing this,

let x = results.compactMap {
    if case .person (let P) = $0 { return P }
    else { return nil }
}

inevitably someone on here can make me look like a fool and show a tighter way to do this in current Swift!

Go for it...

Upvotes: 0

Views: 328

Answers (2)

user3441734
user3441734

Reputation: 17544

maybe define 

func person(_ r: ResultItem)->Person? {
    if case .person (let P) = r { return P }
    else { return nil }
}

and next compact. at least it is easier to read for me ...

let persons = items.compactMap(person)

or even better

extension ResultItem {
    static func person(_ r: ResultItem)->Person? {
        if case .person (let P) = r { return P }
        else { return nil }
    }
}

and

let persons = items.compactMap(ResultItem.person)

Upvotes: 1

matt
matt

Reputation: 535411

So results is an array of ResultItem and the idea is to extract the payloads from only the ones that are Persons?

I don't know if this is "tighter" but I would probably do it with for case let:

let arr : [ResultItem] = // ...
var persons = [Person]()
for case let .person(p) in arr { persons.append(p) }

You might reasonably object: "But I don't want persons to be a var." Yes, I know how you feel. So sometimes I say this instead (wordier, to be sure):

let persons : [Person] = 
    arr.reduce(into: []) {if case let .person(p) = $1 {$0.append(p)}}

They are both really ways of saying the same thing: append only if you can extract a Person. Of course you are doing that same thing, in a way, but the roundabout return nil into a compactMap is probably the objectionable part, and the second formulation is arguably a one-liner, so perhaps that's "tighter".

Upvotes: 2

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