Providing option for Custom Style View Modifier

CustomStyleViewModifier.swift

import SwiftUI


// MARK: 2. Create view style protocol

protocol CardStyle {
  associatedtype Body: View
  typealias Configuration = CardStyleConfiguration
  func makeBody(configuration: Self.Configuration) -> Self.Body
}

// MARK: 3. Create style configuration

struct CardStyleConfiguration {
  /// A type-erased content of a `Card`.
  struct Label: View {
    init<Content: View>(content: Content) {
      body = AnyView(content)
    }

    var body: AnyView
  }

  let label: CardStyleConfiguration.Label
}

// MARK: 4. Implement base view styles

struct DefaultCardStyle: CardStyle {
  func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .font(.title)
      .padding()
      .background(RoundedRectangle(cornerRadius: 16).strokeBorder())
  }
}

struct GradientCardStyle: CardStyle {
    let gradient = AngularGradient(
        gradient: Gradient(colors: [Color.red, Color.green, Color.blue]),
        center: .center)
    
    func makeBody(configuration: Configuration) -> some View {
        configuration.label
            .font(.title)
            .padding()
            .background(RoundedRectangle(cornerRadius: 16).stroke(gradient, lineWidth: 1))
    }
}

// MARK: 6. Setup style environment (key + environment value + style eraser)

struct AnyCardStyle<S: CardStyle>: CardStyle {
    private var _makeBody: (Configuration) -> S.Body

  init(style: S) {
    _makeBody = { configuration in
      style.makeBody(configuration: configuration)
    }
  }

 func makeBody(configuration: Configuration) -> S.Body {
    _makeBody(configuration)
  }
}

struct CardStyleKey: EnvironmentKey {
  static var defaultValue = AnyCardStyle(style: DefaultCardStyle())
}

extension EnvironmentValues {
  var cardStyle: AnyCardStyle<DefaultCardStyle> {
    get { self[CardStyleKey.self] }
    set { self[CardStyleKey.self] = newValue }
  }
}

// MARK: 7. Define `.xxxStyle(_:)` convenience view modifier

extension View {
    func cardStyle(style: any CardStyle = DefaultCardStyle()) -> some View {
        self.modifier(CardModifier(style: style))
    }
}

// MARK: 8. Update view to take advantage of environment style

struct CardModifier: ViewModifier {
    var style: any CardStyle
    public func body(content: Content) -> some View {
       AnyView(style
          .makeBody(
            configuration: CardStyleConfiguration(
              label: CardStyleConfiguration.Label(content: content)
            )
          )
       )
    }
}

// MARK: 9. Enjoy :)

struct TestView: View {
    var body: some View {
        
        Button {
        } label: {
            Text("Hello")
        }
        .cardStyle(style: GradientCardStyle())
    }
}