``++GetHashCode++`` is used to file an object in a ``++Dictionary++`` or ``++Hashtable++``. If ``++GetHashCode++`` uses non-``++readonly++`` fields and those fields change after the object is stored, the object immediately becomes mis-filed in the ``++Hashtable++``. Any subsequent test to see if the object is in the ``++Hashtable++`` will return a false negative.


== Noncompliant Code Example

----
public class Person 
{
  public int age;
  public string name;

  public override int GetHashCode() 
  {
    int hash = 12;
    hash += this.age.GetHashCode(); // Noncompliant
    hash += this.name.GetHashCode(); // Noncompliant
    return hash;
  }
----


== Compliant Solution

----
public class Person 
{
  public readonly DateTime birthday;
  public string name;

  public override int GetHashCode() 
  {
    int hash = 12;
    hash += this.birthday.GetHashCode();
    return hash;
  }
----


