For example, the DOM specification has various IDL definitions, one of which is the Interface Node. How would you go about translating this—even a portion of this—into actual C#? I mean, where would you even start? As far as I understand, C#’s interfaces behave much differently than what IDL is calling an interface here. Am I wrong?
interface Node {
// NodeType
const unsigned short ELEMENT_NODE = 1;
const unsigned short ATTRIBUTE_NODE = 2;
const unsigned short TEXT_NODE = 3;
const unsigned short CDATA_SECTION_NODE = 4;
const unsigned short ENTITY_REFERENCE_NODE = 5;
const unsigned short ENTITY_NODE = 6;
const unsigned short PROCESSING_INSTRUCTION_NODE = 7;
const unsigned short COMMENT_NODE = 8;
const unsigned short DOCUMENT_NODE = 9;
const unsigned short DOCUMENT_TYPE_NODE = 10;
const unsigned short DOCUMENT_FRAGMENT_NODE = 11;
const unsigned short NOTATION_NODE = 12;
readonly attribute DOMString nodeName;
attribute DOMString nodeValue;
// raises(DOMException) on setting
// raises(DOMException) on retrieval
readonly attribute unsigned short nodeType;
readonly attribute Node parentNode;
readonly attribute NodeList childNodes;
readonly attribute Node firstChild;
readonly attribute Node lastChild;
readonly attribute Node previousSibling;
readonly attribute Node nextSibling;
readonly attribute NamedNodeMap attributes;
// Modified in DOM Level 2:
readonly attribute Document ownerDocument;
// Modified in DOM Level 3:
Node insertBefore(in Node newChild,
in Node refChild)
raises(DOMException);
// Modified in DOM Level 3:
Node replaceChild(in Node newChild,
in Node oldChild)
raises(DOMException);
// Modified in DOM Level 3:
Node removeChild(in Node oldChild)
raises(DOMException);
// Modified in DOM Level 3:
Node appendChild(in Node newChild)
raises(DOMException);
boolean hasChildNodes();
Node cloneNode(in boolean deep);
// Modified in DOM Level 3:
void normalize();
// Introduced in DOM Level 2:
boolean isSupported(in DOMString feature,
in DOMString version);
// Introduced in DOM Level 2:
readonly attribute DOMString namespaceURI;
// Introduced in DOM Level 2:
attribute DOMString prefix;
// raises(DOMException) on setting
// Introduced in DOM Level 2:
readonly attribute DOMString localName;
// Introduced in DOM Level 2:
boolean hasAttributes();
// Introduced in DOM Level 3:
readonly attribute DOMString baseURI;
// DocumentPosition
const unsigned short DOCUMENT_POSITION_DISCONNECTED = 0x01;
const unsigned short DOCUMENT_POSITION_PRECEDING = 0x02;
const unsigned short DOCUMENT_POSITION_FOLLOWING = 0x04;
const unsigned short DOCUMENT_POSITION_CONTAINS = 0x08;
const unsigned short DOCUMENT_POSITION_CONTAINED_BY = 0x10;
const unsigned short DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC = 0x20;
// Introduced in DOM Level 3:
unsigned short compareDocumentPosition(in Node other)
raises(DOMException);
// Introduced in DOM Level 3:
attribute DOMString textContent;
// raises(DOMException) on setting
// raises(DOMException) on retrieval
// Introduced in DOM Level 3:
boolean isSameNode(in Node other);
// Introduced in DOM Level 3:
DOMString lookupPrefix(in DOMString namespaceURI);
// Introduced in DOM Level 3:
boolean isDefaultNamespace(in DOMString namespaceURI);
// Introduced in DOM Level 3:
DOMString lookupNamespaceURI(in DOMString prefix);
// Introduced in DOM Level 3:
boolean isEqualNode(in Node arg);
// Introduced in DOM Level 3:
DOMObject getFeature(in DOMString feature,
in DOMString version);
// Introduced in DOM Level 3:
DOMUserData setUserData(in DOMString key,
in DOMUserData data,
in UserDataHandler handler);
// Introduced in DOM Level 3:
DOMUserData getUserData(in DOMString key);
};
Background
In C#, an interface is by definition empty and has many possible implementations. In COM, in general, an interface will have one implementation and defines a calling contract, not an implementation contract (like with web services or CORBA). In C#, the implementation of an interface is .NET specific. In COM, the implementation of an interface is a language-neutral, but a binary implementation (as opposed to SOAP messages, which is textual/XML). This binary definition has always been food for criticasters of COM and the slow (if at all) adoption of COM on non-Windows systems (again, as opposed to web services).
For practically all IDL commands, there’s an equivalent possibility in C#, albeit not always within just in interface. The base interface of COM is always
IUknown, which is used for object reference counting, which must be included by all COM objects.In speech, when talking about a COM interface, you usually talk about an implementation. In c#, you usually talk about the empty contracts that callers and implementers understand.
Translate IDL
The IDL above is for DOM, as you mention. The DOM is implemented in C# and is much more powerful than its COM cousins (and many versions). If you really want to create a C# class wrapper that can call the COM DOM interfaces:
You can also run tlbimp.exe directly on the COM dlls (in process) or executables (out of process) to create a .NET COM Wrapper.
More information
A basic, yet extremely brilliant and thorough introduction to COM is Don Box’s famous book Essential COM, about IDL I suggest Essential IDL by Gudgin.
Absolutely everything there is to know about COM and .NET is written down in the comprehensive, yet slightly bloated, .NET and .COM The Complete Interoperability Guide by Nathan. Not a book you will read from cover to cover, but it makes excellent reference material.