reference-environment.swift

import SwiftUI

class Counter {
  var count = 0
}
extension EnvironmentValues {
  @Entry var counter = Counter()
}

struct ContentView: View {
  @Environment(\.counter) var counter

  var body: some View {
    Form {
      Text("\(counter.count)")
      Button("Increment") {
        counter.count += 1
        print(counter.count)
      }
    }
  }
}

#Preview {
  ContentView()
}