Why should I care about RTTI in Delphi?

Question

I've heard a lot about the new/improved RTTI capabilities of Delphi 2010, but I must admit my ignorance...I don't understand it. I know every version of Delphi has supported RTTI...and I know that RTTI (Runtime Type Information) allows me to access type information while my application is running.

But what exactly does that mean? Is Delphi 2010's RTTI support the same thing as reflection in .NET?

Could someone please explain why RTTI is useful? Pretend I'm your pointy haired boss and help me understand why RTTI is cool. How might I use it in a real-world application?

Answer 1

RTTI in Delphi is still not quite as full-featured as Reflection in .NET or other managed languages, because it is operating on compiled code, not an Intermediate Language (bytecode). However, it is a very similar concept, and the new RTTI system in Delphi 2010 brings it a lot closer to reflection, exposing an entire object-oriented API.

Pre-D2010, the RTTI was pretty limited. About the only thing I ever remember doing with it was converting an enumerated type to a string (or vice versa) for use in drop-down lists. I may have used it at one point for control persistence.

With the new RTTI in D2010 you can do a lot more things:

• XML Serialization

• Attribute-based metadata (TCustomAttribute). Typical use cases would be automatic validation of properties and automated permission checks, two things that you normally have to write a lot of code for.

• Adding Active Scripting support (i.e. using the Windows script control)

• Building a plug-in system; you could do this before, but there were a lot of headaches. I wasn't able to find a really good example of someone doing this from top to bottom, but all of the necessary functions are available now.

• It looks like someone's even trying to implement Spring (DI framework) for Delphi 2010.

So it's definitely very useful, although I'm not sure how well you'd be able to explain it to a PHB; most of its usefulness is probably going to be realized through 3rd-party libraries and frameworks, much the same way it works in the .NET community today - it's rare to see reflection code sitting in the business logic, but a typical app will make use of several reflection-based components like an Object-Relational Mapper or IoC Container.

Have I answered the question?

Answer 2

Most people probably won't use it in a real world application.

The people who will use it are the framework builders. Frameworks such as DUnit make extensive use of RTTI.

With the new RTTI capabilities we should expect to start seeing more advanced frameworks and tools appearing, similar to what is available for .NET. These frameworks will revolutionise your development moreso than RTTI will on it's own.