Ugly Swift

Ugly.swift

import UIKit

enum Name {
	case foo(Foo)
	case bar(Bar)
	
	struct Foo {
		let name: String
	}
	
	struct Bar {
		let count: Int
	}
}

let names = [Name.foo(Name.Foo(name: "hello")), Name.bar(Name.Bar(count: 123)), Name.bar(Name.Bar(count: 999))]

// The goal: to get the first Name.Bar item from names, and more importantly, to make the code readable.

func firstBar_TakeOne(in names: [Name]) -> Name.Bar? {
	if case let .bar(bar) = names.first(where: { name in
		if case .bar(_) = name {
			return true
		}
		return false
	}) {
		return bar
	}
	return nil
}

func firstBar_TakeTwo(in names: [Name]) -> Name.Bar? {
	let initialResult: Name.Bar? = nil
	let result = names.reduce(into: initialResult) { result, name in
		guard result == nil else { return }
		if case let .bar(bar) = name {
			result = bar
		}
	}
	return result
}

if let bar = firstBar_TakeOne(in: names) {
	bar.count
}

if let bar = firstBar_TakeTwo(in: names) {
	bar.count
}

I would personally go with:

if let bar = names.extractFirst({ // from answer above
    guard case let .bar(barVal) = $0 else { // fold all other cases into:
        return nil;
    }
    return barVal;
}) {
    bar.count;
}

because I assume struct Name.Bar's role is nailed down enough; if it isn't, what Jared Sinclair said.

Building on the for-loop solution from @ezfe: you can make the variable binding in the loop condition:

func firstBar(in names: [Name]) -> Name.Bar? {
    for case .bar(let bar) in names {
        return bar
    }
    return nil
}

This will iterate over names until it finds the first .bar(_) value and return its associated value (bound to bar in the loop condition). If names doesn't contain any .bar(_) values it will return nil.

I would tend to reach for something like this:

let firstBar = names
    .lazy
    .compactMap({
        switch $0 {
        case let .bar(bar): bar
        default: nil
        }
    })
    .first;

The combination of .lazy and .first should mean you only iterate as far through the collection as you need to, and the result is an Optional<Name.Bar>.

If you use the asBar or barValue helper values others have contributed above, you could then write it as:

return names.lazy.compactMap(\.asBar).first

and still get nearly optimal performance. A regular for loop will probably be marginally faster for small collections though but not by much.

Watch out, the performance of that construct may surprise you: https://forums.swift.org/t/adding-firstas-to-sequence/36665/17

Ahhhh, overloads fun. 🙃 The first(where: { _ in true }) hack is terrible, too 😂 but if abstracted over and provided with a very good explanatory comment, I guess I could live with it. 🙃