Chapter 3. Runtime Type Information

Delphi’s Integrated Development Environment (IDE) depends on information provided by the compiler. This information, called Runtime Type Information (RTTI), describes some aspects of classes and other types. It’s not a full reflection system such as you find in Java, but it’s more complete than type identifiers in C++. For ordinary, everyday use of Delphi, you can ignore the details of RTTI and just let Delphi do its thing. Sometimes, though, you need to look under the hood and understand exactly how RTTI works.

The only difference between a published declaration and a public declaration is RTTI. Delphi stores RTTI for published fields, methods, and properties, but not for public, protected, or private declarations. Although the primary purpose of RTTI is to publish declarations for the IDE and for saving and loading .dfm files, the RTTI tables include other kinds of information. For example, virtual and dynamic methods, interfaces, and automated declarations are part of a class’s RTTI. Most types also have RTTI called type information. This chapter explains all the details of RTTI.

Virtual Method Table

The Virtual Method Table (VMT) stores pointers to all the virtual methods declared for a class and its base classes. The layout of the VMT is the same as in most C++ implementations (including Borland C++ and C++ Builder) and is the same format required for COM, namely a list of pointers to methods. Each virtual method of a class or its ancestor ...

Get Delphi in a Nutshell now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.