using System;

namespace EqualityWithBiDirectionalAssociation
{

    public class Person : IEquatable<Person>
    {
        private string _firstName;
        private string _lastName;
        private Address _address;

        public Person(string firstName, string lastName, Address address)
        {
            FirstName = firstName;
            LastName = lastName;
            Address = address;
        }

        public virtual Address Address
        {
            get { return _address; }
            set { _address = value; }
        }

        public virtual string FirstName
        {
            get { return _firstName; }
            set { _firstName = value; }
        }

        public virtual string LastName
        {
            get { return _lastName; }
            set { _lastName = value; }
        }

        public override bool Equals(object obj)
        {
            // Use 'as' rather than a cast to get a null rather an exception
            // if the object isn't convertible
            Person person = obj as Person;
            return this.Equals(person);
        }

        public override int GetHashCode()
        {
            string composite = FirstName + LastName;
            return composite.GetHashCode();
        }


        #region IEquatable<Person> Members

        public virtual bool Equals(Person other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return (this.Address.Equals(other.Address)
                && this.FirstName.Equals(other.FirstName)
                && this.LastName.Equals(other.LastName));
        }

        #endregion

    }

    public class Address : IEquatable<Address>
    {
        private string _streetName;
        private string _city;
        private string _state;
        private Person _resident;

        public Address(string city, string state, string streetName)
        {
            City = city;
            State = state;
            StreetName = streetName;
            _resident = null;
        }

        public virtual string City
        {
            get { return _city; }
            set { _city = value; }
        }

        public virtual Person Resident
        {
            get { return _resident; }
            set { _resident = value; }
        }

        public virtual string State
        {
            get { return _state; }
            set { _state = value; }
        }

        public virtual string StreetName
        {
            get { return _streetName; }
            set { _streetName = value; }
        }

        public override bool Equals(object obj)
        {
            // Use 'as' rather than a cast to get a null rather an exception
            // if the object isn't convertible
            Address address = obj as Address;
            return this.Equals(address);
        }

        public override int GetHashCode()
        {
            string composite = StreetName + City + State;
            return composite.GetHashCode();
        }


        #region IEquatable<Address> Members

        public virtual bool Equals(Address other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return (this.City.Equals(other.City)
                && this.State.Equals(other.State)
                && this.StreetName.Equals(other.StreetName)
                && this.Resident.Equals(other.Resident));
        }

        #endregion
    }

    public class Program
    {
        static void Main(string[] args)
        {
            Address address1 = new Address("seattle", "washington", "Awesome St");
            Address address2 = new Address("seattle", "washington", "Awesome St");

            Person person1 = new Person("John", "Doe", address1);

            address1.Resident = person1;
            address2.Resident = person1;

            if (address1.Equals(address2)) // <-- Generates a stack overflow!
            {
                Console.WriteLine("The two addresses are equal");
            }

            Person person2 = new Person("John", "Doe", address2);
            address2.Resident = person2;

            if (address1.Equals(address2)) // <-- Generates a stack overflow!
            {
                Console.WriteLine("The two addresses are equal");
            }

            Console.Read();
        }
    }
}

using System;

namespace EqualityWithBiDirectionalAssociation
{

    public class Person : IEquatable<Person>
    {
        private string _firstName;
        private string _lastName;
        private Address _address;

        public Person(string firstName, string lastName, Address address)
        {
            FirstName = firstName;
            LastName = lastName;
            Address = address;
        }

        public virtual Address Address
        {
            get { return _address; }
            set { _address = value; }
        }

        public virtual string FirstName
        {
            get { return _firstName; }
            set { _firstName = value; }
        }

        public virtual string LastName
        {
            get { return _lastName; }
            set { _lastName = value; }
        }

        public override bool Equals(object obj)
        {
            // Use 'as' rather than a cast to get a null rather an exception
            // if the object isn't convertible
            Person person = obj as Person;
            return this.Equals(person);
        }

        public override int GetHashCode()
        {
            string composite = FirstName + LastName;
            return composite.GetHashCode();
        }

        internal virtual bool EqualsIgnoringAddress(Person other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return ( this.FirstName.Equals(other.FirstName)
                && this.LastName.Equals(other.LastName));
        }

        #region IEquatable<Person> Members

        public virtual bool Equals(Person other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return (this.Address.EqualsIgnoringPerson(other.Address)   // Don't have Address check it's person
                && this.FirstName.Equals(other.FirstName)
                && this.LastName.Equals(other.LastName));
        }

        #endregion

    }

    public class Address : IEquatable<Address>
    {
        private string _streetName;
        private string _city;
        private string _state;
        private Person _resident;

        public Address(string city, string state, string streetName)
        {
            City = city;
            State = state;
            StreetName = streetName;
            _resident = null;
        }

        public virtual string City
        {
            get { return _city; }
            set { _city = value; }
        }

        public virtual Person Resident
        {
            get { return _resident; }
            set { _resident = value; }
        }

        public virtual string State
        {
            get { return _state; }
            set { _state = value; }
        }

        public virtual string StreetName
        {
            get { return _streetName; }
            set { _streetName = value; }
        }

        public override bool Equals(object obj)
        {
            // Use 'as' rather than a cast to get a null rather an exception
            // if the object isn't convertible
            Address address = obj as Address;
            return this.Equals(address);
        }

        public override int GetHashCode()
        {
            string composite = StreetName + City + State;
            return composite.GetHashCode();
        }



        internal virtual bool EqualsIgnoringPerson(Address other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return (this.City.Equals(other.City)
                && this.State.Equals(other.State)
                && this.StreetName.Equals(other.StreetName));
        }

        #region IEquatable<Address> Members

        public virtual bool Equals(Address other)
        {
            // Per MSDN documentation, x.Equals(null) should return false
            if ((object)other == null)
            {
                return false;
            }

            return (this.City.Equals(other.City)
                && this.State.Equals(other.State)
                && this.StreetName.Equals(other.StreetName)
                && this.Resident.EqualsIgnoringAddress(other.Resident));
        }

        #endregion
    }

    public class Program
    {
        static void Main(string[] args)
        {
            Address address1 = new Address("seattle", "washington", "Awesome St");
            Address address2 = new Address("seattle", "washington", "Awesome St");

            Person person1 = new Person("John", "Doe", address1);

            address1.Resident = person1;
            address2.Resident = person1;

            if (address1.Equals(address2)) // <-- No stack overflow!
            {
                Console.WriteLine("The two addresses are equal");
            }

            Person person2 = new Person("John", "Doe", address2);
            address2.Resident = person2;

            if (address1.Equals(address2)) // <-- No a stack overflow!
            {
                Console.WriteLine("The two addresses are equal");
            }

            Console.Read();
        }
    }
}

public override bool Equals(object obj){
// Use 'as' rather than a cast to get a null rather an exception
// if the object isn't convertible           .
Person person = obj as Person;
return this.Equals(person);        // wrong
this.FirstName.Equals(person.FirstName)
this.LastName.Equals(person.LastName)
// and so on
}