Foundations of Programming - Karl Seguin

Chapter 7 - Back to Basics: Memory
ByRef
Without a good understanding of pointers, it's virtually impossible to understand passing a value by
reference and by value. Developers generally understand the implication of passing a value type, such as
an integer, by reference, but few understand why you'd want to pass a reference by reference. ByRef
and ByVal affect reference and value types the same - provided you understand that they always work
against the underlying value (which in the case of a reference type means they work against the pointer
and not the value). Using ByRef is the only common situation where .NET won't automatically resolve
the pointer indirection (passing by reference or as an output parameter isn't allowed in Java).
First we'll look at how ByVal/ByRef affects value types. Given the following code:
public static void Main()
{
int counter1 = 0;
SeedCounter(counter1);
Console.WriteLine(counter1);
}
int counter2 = 0;
SeedCounter(ref counter2);
Console.WriteLine(counter2);
private static void SeedCounter(int counter)
{
counter = 1;
}
private static void SeedCounter(ref int counter)
{
counter = 1;
}
We can expect an output of 0 proceeded by 1. The first call does not pass counter1 by reference,
meaning a copy of counter1 is passed into SeedCounter and changes made within are local to the
function. In other words, we're taking the value on the stack and duplicating it onto another stack
location.
In the second case we're actually passing the value by reference which means no copy is created and
changes aren't localized to the SeedCounter function.
The behavior with reference types is the exact same, although it might not appear so at first. We'll look
at two examples. The first one uses a PayManagement class to change the properties of an Employee.
In the code below we see that we have two employees and in both cases we're giving them a $2000
raise. The only difference is that one passes the employee by reference while the other is passed by
value. Can you guess the output?
Foundations of Programming Copyright © Karl Seguin www.codebetter.com
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