Foundations of Programming - Karl Seguin

Chapter 7 - Back to Basics: Memory
public class Employee
{
private int _salary;
public int Salary
{
get {return _salary;}
set {_salary = value;}
}
public Employee(int startingSalary)
{
_salary = startingSalary;
}
}
public class PayManagement
{
public static void Terminate(Employee employee)
{
employee = null;
}
public static void Terminate(ref Employee employee)
{
employee = null;
}
}
public static void Main()
{
Employee employee1 = new Employee(10000);
PayManagement.Terminate(employee1);
Console.WriteLine(employee1.Salary);
}
Employee employee2 = new Employee(10000);
PayManagement.Terminate(ref employee2);
Console.WriteLine(employee2.Salary);
Try to figure out what will happen and why. I'll give you a hint: an exception will be thrown. If you
guessed that the call to employee1.Salary outputted 10000 while the 2nd one threw a
NullReferenceException then you're right. In the first case we're simply setting a copy of the
original pointer to null - it has no impact whatsoever on what employee1 is pointing to. In the second
case, we aren't passing a copy but the same stack value used by employee2. Thus setting the employee
to null is the same as writing employee2 = null;.
It's quite uncommon to want to change the address pointed to by a variable from within a separate
method - which is why the only time you're likely to see a reference type passed by reference is when
you want to return multiple values from a function call (in which case you're better off using an out
parameter, or using a purer OO approach). The above example truly highlights the dangers of playing in
an environment whose rules aren't fully understood.
Foundations of Programming Copyright © Karl Seguin www.codebetter.com
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