A simple picker to pick a enum.

EnumPicker.swift

import SwiftUI

struct EnumPicker<T: Hashable & CaseIterable, V: View>: View {
    
    @Binding var selected: T
    var title: String? = nil
    
    let mapping: (T) -> V
    
    var body: some View {
        Picker(selection: $selected, label: Text(title ?? "")) {
            ForEach(Array(T.allCases), id: \.self) {
                mapping($0).tag($0)
            }
        }
    }
}

extension EnumPicker where T: RawRepresentable, T.RawValue == String, V == Text {
    init(selected: Binding<T>, title: String? = nil) {
        self.init(selected: selected, title: title) {
            Text($0.rawValue)
        }
    }
}

It is really simple to use if you have a case iterable enum with a raw value of String:

enum PickerAction: String, CaseIterable {
  case source, targets
}

Just simply:

struct ContentView: View {
    @State private var pickerAction = PickerAction.source
    var body: some View {
      EnumPicker(selected: $pickerAction)
    }
}

As it will produce a Text-view itself; but if your enum does not have such string as a raw value, you can return a view in a closure:

EnumPicker(selected: $pickerAction) { e in
  // return view here
}

and you can of course also change the picker style, just add it to the environment: (Thanks @tobiasdm)

var body: some View {
  EnumPicker(selected: $pickerAction)
    .pickerStyle(SegmentedPickerStyle())
}

PS: If you rely on a custom view instead of the string value, remember that SegmentedPickerStyle can only show one Image or one Text-view per segment.

It works great.

But in most cases, the raw values of the enums are not good enough to be displayed to the user and in some cases, we have Int as raw values. So I wrote another extension.

extension EnumPicker where T: Displayable, V == Text {
    init(selected: Binding<T>, title: String? = nil) {
        self.init(selected: selected, title: title) {
            Text($0.displayValue)
        }
    }
}

protocol Displayable {
    var displayValue: String { get }
}

This works great.

The only change I made is to use Apple's standard CustomStringConvertable protocol instead of Displayable.

extension EnumPicker where T: CustomStringConvertible, V == Text {
    
    init(_ title: String? = nil, selected: Binding<T>) {
        self.init(title: title, selected: selected) {
            Text($0.description)
        }
    }
}

Thanks @lstomberg!

And yes, it is always great to use things from the Swift Standard Library, good think 💪🏼💪🏼

Instead of extensions, you can use a simplified version with a default "displayer", note no need for RawRepresentable, just Hashable and CaseIterable

struct CaseIterablePicker<T: CaseIterable & Hashable> : View
  where T.AllCases: RandomAccessCollection {

  var title: String = ""
  var selection: Binding<T>
  var display: (T) -> String = { "\($0)" }

  var body: some View {
    Picker(title, selection: selection) {
      ForEach(T.allCases, id:\.self) {
        Text(display($0)).tag($0)
      }
    }
  }
}

You can pass closures to display, or KeyPath's with Swift 5.2+, which allows the following, which IMO is better as it simplifies the generic definition greatly and moves the burden on "how to display stuff" to the caller, but in a pretty easy to manage manner

// Simple case, use existing string transforms
enum TestEnum: String, CaseIterable {
  case one, two, three, four, five
}

CaseIterablePicker(selection: $testEnum, display: \.rawValue.capitalized) // Options show as "One", "Two", "Three"...

// Custom extension to String for camel case transform
enum TestEnum2: String, CaseIterable {
  case aTestCase, anotherTestCase, thirdTestCase
}

extension String {
  var camelCaseToReadable: String { ... }
}
CaseIterablePicker(selection: $testEnum2, display: \.rawValue.camelCaseToReadable.capitalizingFirstLetter)
// long chained KeyPath, options show as "A test case", "Another test case", "Third test case"

// Computed var on enum itself is just as simple and doesn't even require RawRepresentable
enum TestEnum3: CaseIterable {
  case someCase, anotherCase, whatever
  
  var localized: LocalizedStringKey { ... }
}

CaseIterablePicker(selection: $testEnum2, display: \.localized)

Hey @apocolipse!
That is also a take on using enum for pickers. If a simple text view is what always is needed, I think it is a great solution, however it misses the view flexibility of my version :-)

Also, the best of both world can be done! See this extension for my version:

extension EnumPicker where V == Text {
    init(selected: Binding<T>, title: String? = nil, display: @escaping (T) -> String) {
        self.init(selected: selected, title: title) {
            Text(display($0))
        }
    }
}