How to use View protocol in SwiftUI

Issue #791

SwiftUI has View protocol which represents part of your app’s user interface and provides modifiers that you use to configure views.

You create custom views by declaring types that conform to the View protocol. Implement the required body computed property to provide the content for your custom view.

A typical example of View is using struct

enum HeroType {
    case melee
    case range
}

struct ContentView: View {
    let heroType: HeroType

    var body: some View {
        switch heroType {
        case .melee: Text("Melee")
        case .range: Text("Range")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView(heroType: .melee)
    }
}

But were are not limited to using struct, we can use enum or class if we need to. For example here I use enum that has body method

enum HeroView: View {
    case melee
    case range

    var body: some View {
        switch self {
        case .melee: Text("Melee")
        case .range: Text("Range")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        HeroView.melee
    }
}

Note that if you use class

final class ContentView: View {

}

SwiftUI will crash because it expects only value types like struct and enum

Fatal error: views must be value types