Value types can be separated in three main types:
- Built in types (these are the types with which other types are built)
- User defined types (structures)
- Enumerations (related symbols that have fixed values)
Declaring value types
- Using a type requires to declare a symbol as an instance of that type.
- VT have an implicit constructor (new keyword is not necessary as you do with classes).
- Default constructor assigns a default value (usually null or zero)
Example (C#):
bool symboName = true;
Nullable
When you work with reference types you can see if the object is null to see if the valuye contains something, in the VT you cannot assign a null reference point to a value type.
To let yo know wheter a value has not been assigned you can declare the variable as nullable (the classic example is an answer for a question (Yes/No), when do you know if the question has been answered?)
Nullable
or
bool? answer=null; //Shorthand notation
When you declare a VT as nullable it enables the HasValue and Value members (you can use them for validation purposes)
if (answer.HasValue)
doSomething();
User-Defined types.
Commonly called structures. Like other value types these are stored in the stack and they contain their data directly. The structures behave nearly identical to classes.
Structs are a composite of other types that make ir easier to work with related data.
example of structure:
System.Drawing.Point p = new System.Drawing.Point(20,30);
Declaring an structure.
struct Person
{
DateTime _birth;
string _name;
public Cycle(birth, name)
{
doSomething();
}
}
Structures are usually more efficient than classes if the type meets all of these criteria.
- Logically represents a single value
- Has an instance size less than 16b
- Will not be changed after reation, and will not be casted to a reference type.
Enumerations
The enumerations are related symbos that have fized values, you can provide a list of choices for developers with an enumeration.
The enums simplify coding an improve code readability by enabling you to use meaningful symbols instead of simple numeric valuyes.
Example.
enum titles : int {Mr, Mrs, Ms, Dr};
