C# 4 and .NET 4

80 ❘ ChaPTer 3 Objects And types
sTruCTs
So far, you have seen how classes offer a great way of encapsulating objects in your program. You have also
seen how they are stored on the heap in a way that gives you much more flexibility in data lifetime, but with
a slight cost in performance. This performance cost is small thanks to the optimizations of managed heaps.
However, in some situations all you really need is a small data structure. In this case, a class provides more
functionality than you need, and for performance reasons you will probably prefer to use a struct. Look at
this example:
class Dimensions
{
public double Length;
public double Width;
}
This code defines a class called Dimensions, which simply stores the length and width of an item.
Perhaps you’re writing a furniture-arranging program to let people experiment with rearranging
their furniture on the computer, and you want to store the dimensions of each item of furniture.
It looks as though you’re breaking the rules of good program design by making the fields public, but
the point is that you don’t really need all the facilities of a class for this. All you have is two numbers,
which you’ll find convenient to treat as a pair rather than individually. There is no need for a lot of
methods, or for you to be able to inherit from the class, and you certainly don’t want to have the
.NET runtime go to the trouble of bringing in the heap with all the performance implications, just
to store two doubles.
As mentioned earlier in this chapter, the only thing you need to change in the code to define a type as a
struct instead of a class is to replace the keyword class with struct:
struct Dimensions
{
public double Length;
public double Width;
}
Defining functions for structs is also exactly the same as defining them for classes. The following code
demonstrates a constructor and a property for a struct:
struct Dimensions
{
public double Length;
public double Width;
}
public Dimensions(double length, double width)
{
Length=length;
Width=width;
}
public double Diagonal
{
get
{
return Math.Sqrt(Length*Length + Width*Width);
}
}
Structs are value types, not reference types. This means they are stored either in the stack or inline (if they
are part of another object that is stored on the heap) and have the same lifetime restrictions as the simple
data types.
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