C# ValueType Examples: Int, DateTime

ValueType. Indirection measures steps needed to load a value.

Reference types add indirection. They point to another memory location. Value types do not. They are self-contained, often in the bytes on the evaluation stack.

Example. First, this program shows an int value type. Please notice that no constructor is used on the int. It is stored entirely within stack memory space. The managed heap is not touched. No allocation occurs there.

Also: When a number is added to the int, that memory location's value is changed. No new int is created as a result of the addition.

Tip: Using value types, instead of reference types, is often a good optimization. There are counterexamples: large structs can be slower.

Optimizations

C# program that demonstrates value type

using System;

class Program
{
    static void Main()
    {
	int value = 10;
	value += DateTime.Today.Day;
	Console.WriteLine(value);
    }
}

Output

15

Types. Value types are used constantly in C# programs. Even a simple for-loop uses an int value type to iterate. And floating-point values, such as doubles, can represent important (and large) numbers.

boolbytechardecimaldoublefloatintlongshort

Structs: All values are considered structs. A struct is simply a region of bytes that can be accessed. These bytes represent values.

Struct

Class. The ValueType class is a base class for all value types, which include ints, shorts, doubles, and also structs such as DateTime instances. Next we use ValueType to refer to these values, and also as a parameter type in methods.

C# program that uses ValueType

using System;

class Program
{
    static ValueType _valueType = false;

    static void Main()
    {
	// You can refer to System.Int32 as a ValueType.
	ValueType type1 = 5;
	Console.WriteLine(type1.GetType());

	// You can refer to System.DateTime as a ValueType.
	ValueType type2 = DateTime.Now;
	Console.WriteLine(type2.GetType());

	// You can refer to System.Boolean as a ValueType.
	Console.WriteLine(_valueType.GetType());

	// Pass as parameter.
	Method(long.MaxValue);
	Method(short.MaxValue);
    }

    static void Method(ValueType type)
    {
	Console.WriteLine(type.GetType());
    }
}

Output

System.Int32
System.DateTime
System.Boolean
System.Int64
System.Int16

ValueType is a class, which means it is not actually a value type itself. Because it is the base class for values, you can refer to those values through a ValueType reference variable.

Above: We showed ValueTypes that were actually ints, DateTime structs, and bool fields.

Finally: We showed how you can use the ValueType type as a parameter to a method.

Next, what is the practical use of a ValueType parameter? It is a way to require that an argument is a value type. You can accept any argument with an object parameter, but it may be useful to further constrain the argument.

Object: This is the base class for all types. In this way it is similar to ValueType, but ValueType too is a subclass of object.

Object Type

Base class. The ValueType class may be useful in some narrow cases in actual programs. I have never needed it. But it is important as a base class for actual value types. This is why it has no constructor.

Usually: You should use the actual value types (such as int, long, short, DateTime) and not bother with ValueType itself.

DateTime

Blittable types. One concept that is related to value types is blittable types. A blittable type is compatible to an unmanaged type. Programs that use blittable types do not need to convert them before passing them to an unmanaged DLL.

In the book Expert .NET 2.0 IL Assembler we learn more about blittable types. In the .NET Framework some types, such as signed and unsigned integers, are blittable (page 371). They require no special conversion.

Bool: This type is sometimes not blittable. Some unmanaged systems require a four-byte boolean.

Char: This is also sometimes not blittable. It may need to be converted to an ANSI (1-byte) character.

Many developers do not care about the blittable status of their values. But it is worthwhile knowing that some value types are not blittable and would need special conversions. This is helpful, particularly in interoperation.

Summary. A variable stores a value. In programs, even a reference (pointer) is a value. It is simply a value that points to another value. The ValueType class is an important detail: it serves as an abstract base class for all value types.

But: Applications focus on the value types themselves. These include int, long, short and DateTime.

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