Creating custom bindings for an element inside a collection.

PeopleList.swift

import SwiftUI

struct Person: Identifiable {
    let id = UUID()
    
    var firstName: String
    var lastName: String
}

struct PersonField: View {
    @Binding var person: Person

    var body: some View {
        HStack {
            TextField("First Name", text: $person.firstName).border(Color.black)
            TextField("Last Name", text: $person.lastName).border(Color.black)
        }
    }
}

struct PeopleList: View {
    @State var people: [Person]
    
    func personIndex(_ person: Person) -> Int {
        people.firstIndex(where: { $0.id == person.id })!
    }

    var body: some View {
        VStack {
            List {
                ForEach(people) { person in
                    PersonField(person:
                        Binding(
                            get: { person },
                            set: { updatedPerson in
                                self.people[self.personIndex(updatedPerson)] = updatedPerson
                        })
                    )
                }
            }

            ForEach(people) { person in
                Text("\(person.firstName) \(person.lastName)")
            }
        }
    }
}

struct PeopleList_Previews: PreviewProvider {
    static var previews: some View {
        PeopleList(people: [
            Person(firstName: "Kurt", lastName: "Mueller"),
            Person(firstName: "Dustin", lastName: "Perzanowski"),
            Person(firstName: "Chris", lastName: "Guard")
        ])
    }
}