Should Class Helpers be used in developing new cod

Question

Delphi 8 introduced Class Helpers for the purposes of mapping the VCL/RTL to the .NET object hierarchy. They allow injecting methods into an existing class without overriding the the class or modifying the original. Later versions of Delphi found class helpers improved and they were ported to Win32.

In the help it says "they should not be viewed as a design tool to be used when developing new code."

Class Helpers violate traditional OOP, but I don't think that makes them a bad thing. Is this warning warranted?

Should class helpers be used when developing new code?

Do you use them when developing new code?

Why or why not?

Per Malcolm's comments: New code means daily application development, where you have some 3rd party libraries, some existing code, and then code you are writing.

Answer 1

I find myself using them more and more as a design construct.

Situations in which I use them :

• In a client/server setup, I extend shared base-classes with class helpers to provide server- or client-only functionality.
• To complement VCL/RTL classes (and other third party code) with handy tooling functions.
• To work around differences when classes don't share the same inheritance tree (using helpers makes it possible to have have generic Count and Items properties, for example).

In fact, I wish Delphi would accept multiple helpers for the same base class - I've even filed a request for this if I'm remembering correctly.

Answer 2

I agree with Vegar in this: class helpers as a emergency tool. When you know they are the only way to get things done in the time provided. Later, if there's time to it, remove them.

I one time forgot a parametrization thing, and if class helpers didn't exist in Delphi 2006 it would cost A ENORMOUS LOT OF TIME..... With class helpers, it took 6 hours to make thigs work right. BUT, it was an emergency situation - class helpers are an obscure language feature and it create difficulties to new developers to follow the flow of the program.

Answer 3

Before embracing class helpers as a new tool for fancy code, I think you have to understand the limitations is includes. There is only possible to provide one class helper for one class. So what will happen if you provide class helpers for your classes, and your classes derives from a common class that some other have provided a class helper for?

CodeGear introduces class helpers as 'a hack' to prevent breaking things, not as a cool design feature. When you design code, design it without class helpers. I know you can. When dealing with existing code that you can control, use refactoring. When there is no other way, reach for class helpers.

Thats my opinion any way...

Answer 4

I found this article very interesting. It deals with C++ but the main ideas are language independent. The main gist is that global routines are sometimes preferrable to methods even in an OOP environment. From this view point, there's less need for class helpers.