map(_:) KeyPath as transforming operator

MapKeyPath.swift

struct Person {
    let firstName: String
    let lastName: String
}

let publisher = PassthroughSubject<Person, Never>()

publisher
    .map(\.firstName, \.lastName).sink {
    print("\($0) \($1)")
}
let person = Person(firstName: "Jackie", lastName: "Chan")
publisher.send(person)
// Output:
//  Jackie Chan