Re: Extension suggestions

[Eric Christopher <echristo at cygnus dot com>]

ivan@shadow.sk (Ivan Schreter) writes:

> What is a property? Property is an extension of a field. Properties can
> be read-only, write-only or read-write. They serve for protecting class'
> fields from invalid accesses and can trigger actions on property read or
> write. Anyway, they are a neat thing. Consider this code:
> 
[snip]
> 
> Circle test;
> 
> test.radius = 5;
> 
> Now, you can access the radius of the circle using test.radius. When you set
> test.radius, it will actually generate call to setRadius(rvalue). When you read
> test.radius, it will generate read of private field f_radius. Or, there might
> be a function returning int associated with read, so read would call that
> function and return computed value. This way, some fields can be actually
> computed.
> 

Okay.  IMHO this is a very bad example.  Basically what you are allowing 
the property to do is violate the privateness of the f_radius member by
allowing other outside access than the protected routines that you already
had.

> As for default, it was in C++ Builder intended for builder API, so that
> visual (and other) components are initialized correctly when created. It
> might not be needed for the first implementation... Borland has also some
> more specifiers for property descriptions.
> 

Essentially this originated in Delphi allowing people in a GUI to set
public:, protected:, and private: without having to code.  If you are
just writing code then property is pretty much useless and could originate
in mistakes (IMHO of course) like the above snippet.  I see some of the
usefulness that you see in these, but I can't really see how this would
be an advantage over properly thought out access routines?  

I took a look at another example in C++ Builder also (cgrid.h), the main
use that I've seen it in there is for other objects to request information,
essentially duplicating a method that does the same thing.

-eric