IDL – Constructed Types (User-defined datatypes)
- Combine other types to enable the creation of user-defined data types.
a) enumerated type
- The enumerated type, enum allows the creation of types that can hold one of a set of predefined value specified by the enum.
- Although the identifiers in the enumeration comprise an ordered list, IDL does not specify the ordinal numbering for the identifiers.
- This is similar to enum in C and C++
Ex:
enum DaysOfWeek
{
Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
};
b) structure type
- Contains any no. of member values of disparate types
- Structures are useful in IDL because, unlike CORBA objects, structures are passed by value rather than by reference.
- In other words, when a struct is passed to a remote object, a copy of that struct’s value is created and marshaled to the remote object.
Ex:
struct DateStruct
{
short year,
short month,
short day,
short hour,
short minute,
short second,
short microsecond
};
c) union type
- Represents values of different types.
- Resembles a cross between a C/C++ union and a case statement.
Ex:
union MultipleType switch(long)
{
case 1:
short myShortType;
case 2:
double myDoubleType;
case 3:
default:
string myStringType;
};
- Here, the parameter is called as discriminator.
- A discriminator used in an IDL union is a parameter that determines the value used by the union. The constant values in the case statements must match the discriminator’s type.
