Researching XPIDL and IDL Technologies

Introduction

XPIDL stands for XP Interface Description Language. It is a specification for XPCOM which is a cross platform adapter description language. An adapter description language is used to describe an adapter which unrelated with its machine language. The description of the adapter can use specialized tools to handle automatoc generation of language that is unrelated to the adapter's specifications. Typically XPIDL is frequently used to generate C++ header files and typelib information.

Language

Interfaces

  An interface is declared with the interface keyword, and the simplest possible interface is  
 interface nsToolbar {
 };

To specify an interface's parent, follow the interface name with a colon and the parent name

interface nsIToolbar : nsIParent {
};

Methods

An interface can have both methods and attributes. Attributes are properties of interface objects that can be read and optionally set. The following example - Attributes, properties of interface objects, can be read and optionally set. - This is an example of an interface with one method (no return value, no parameters) named fun and an integer-valued attribute named attr

interface nsIFoo {
  attribute long attr;
  void fun();
};

Methods can have any number of in, out or inout parameters, with a variety of types.

In this example many parameters of different types and in an out specifications are seen

interface nsIStringStuff {
  void findStringLength(in string str, out long l);
  void concatenateStrings(in string str1, in string str2,
                         out string result);
  void replaceChar(inout string str, in char from, in char to,
                  in boolean foldCase);
};

Attributes can be made read-only, by placing the read-only keyword infront of the the definition

interface nsIThing {
  readonly attribute string lookButDontTouch;
};
C++ get and set methods for attributes are automatically declared for attributes in the   
interface. For example attribute name foo generates accessor methods GetFoo and SetFoo.

Built In Types

Type                    C++ 

void 	                void

boolean 	        PRBool

octet 	                PRUint8

short 	                PRInt16

long 	                PRInt32

long long 	        PRInt64

unsigned short 	        PRUint16

unsigned long 	        PRUint32

unsigned long long 	PRUint64

float 	                   float

double 	                  double