Marshaling

Data passed from .NET to the COM component and the other way around must be converted to the corresponding representation. This mechanism is also known as marshaling. What happens here depends on the data type of the data that is passed: you have to differentiate between blittable and non-blittable data types.

Blittable data types have a common representation with both .NET and COM, and no conversion is needed. Simple data types such as byte, short, int, long, and classes and arrays that only contain these simple data types belong to the blittable data types. Arrays must be one-dimensional to be blittable.

A conversion is needed with non-blittable data types. The following table lists some of the non-blittable COM data types with their .NET-related data types. Non-blittable types have a higher overhead because of the conversion.

COM Data Type	.NET Data Type
SAFEARRAY	Array
VARIANT	Object
BSTR	String
IUnknown*, IDispatch*	Object