let inputJson: String = """
[{"firstName":"Jonathan","lastName":"Lovatt","age":33},{"firstName":"Jamie","lastName":"Smith","age":40}]
"""

class Person: Codable {
    var firstName: String
    var lastName: String
    var age: Int

    func printName() -> String {
        return "\(self.firstName) \(self.lastName) is \(self.age)"
    }
}

import Foundation
let d = JSONDecoder()
let myPerson = try! d.decode([Person].self, from: inputJson.data(using: .utf8)!)
for p in myPerson {
    p.printName()
}