Value Types
Part of my 2008 study notes for exam 70-536 (.NET Framework 2.0).
Overview
- Stored on the stack.
- Contain a value, not a reference.
- Inherit from System.Value
- Exists of built-in types, user-defined types and enumerations.
- Prefer to use Int32 (int) and Double (double) for counters/floating numbers. These are optimized by the framework/hardware.
- Nullable types have .HasValue and .Value properties to determine if they have been set.
- Console.WriteLine( (myBool.HasValue) ? myBool.Value.ToString() : “not set” );
- Structures are value types as well, user-defined value types.
- Enums are stored as value types, and primarily used for code readability.
- object.GetType().IsValueType returns true for value types.
Good practice
- Always define the value of a value type upon declaration.
- Initialize it to null if needed.
- The use of nullable types can help to enable bool variables to store null.
- Nullable<bool> myBool = null;
- bool? myBool = null;
- Read Nullable<T> Usage Guidelines however, to avoid using a bool as a tri-state switch.
- Use structures for objects which represent a single combined value, which is smaller then 16 bytes.
- Structures should be immutable.
- Don’t define a default constructor on a structure.
Examples
Value types vs Reference types
// ---------------------------------------------------------------------------------------------
// Example of value types holding a value instead of a reference.
// ---------------------------------------------------------------------------------------------
int a, b;
a = 5; // Store 5 in a
b = a; // Copy the value of a into b, instead of holding a reference
a = 10; // Store 10 in a, will not affect the value of b, since it's been copied.
Console.WriteLine(a); // Will print 10
Console.WriteLine(b); // Will print 5
Nullable Types
Nullable<bool> myBool = null;
Console.WriteLine((myBool.HasValue) ? myBool.Value.ToString() : "not set");
myBool = true;
Console.WriteLine((myBool.HasValue) ? myBool.Value.ToString() : "not set");
Structures
struct MyPoint
{
private int _x;
private int _y;
public int X
{
get { return this._x; }
}
public int Y
{
get { return this._y; }
}
public MyPoint(int x, int y)
{
this._x = x;
this._y = y;
}
}
Enums
enum TestEnum : int
{
Value1,
Value2
}
static void Main(string[] args)
{
TestEnum en = TestEnum.Value1;
Console.WriteLine((int)en + " : " + en);
}
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