odersky-example.ts

class Person {
  constructor(public name : string) { }
}

class Employee extends Person {
  constructor(name: string, public employer: Employer) {
    super(name);
  }
}

class Employer extends Person {
  public employees: Array<Employee>;
  constructor(name: string) {
    super(name);
    this.employees = new Array<Employee>();
  }
  employ(employee: Employee) {
    employee.employer = this;
    this.employees.push(employee);
  }
}

function getEmployers(employees: Array<Employee>): Array<Employer> {
  return employees.map(e => e.employer);
}

var people = new Array<Person>();
people.push(new Person('Jim'));
people.push(new Person('Jane'));
people.push(new Person('Bob'));

var employers = getEmployers(people);

// error TS2082: Supplied parameters do not match any signature of call target:
//   Type 'Person' is missing property 'employer' from type 'Employee'.
// error TS2087: Could not select overload for 'call' expression.