ITT VIS had several presentations about IDL 8.0 at this week's IDL User Group Meeting. David Fanning [says](http://groups.google.com/group/comp.lang.idl-pvwave/browse_thread/thread/d4d7f62842eeabf8#):
> Just one word: Wow!
> It appears that the promise of IDL 5 has finally been realized. :-)
David also [posted a longer description of the new features](http://groups.google.com/group/comp.lang.idl-pvwave/browse_thread/thread/3bc529e6bcd9e83c#), so I won't go through the laundry list (but I do intend to run through it with some examples when 8.0 is actually released, like I did for 7.1).
But I will discuss a bit the one feature that I have used extensively: operator overloading. This was the main focus of [my talk](http://michaelgalloy.com/2010/02/25/gpulib-with-idl-8-0-slides.html) about [GPULib](http://gpulib.txcorp.com) with IDL 8.0. The gist is that GPULib variables will be objects and if you are running IDL 8.0+, you can do things like the following:
IDL> a = gpuFindgen(10)
IDL> b = gpuFindgen(10)
IDL> c = a + b
This was easy to implement, just inherit from `IDL_Object` and write a method with the special name `_overloadPlus`:
function gpuvariable::_overloadPlus, left, right
return, gpuAdd(left, right)
Most operators are supported like `+`, `-`, `/`, `*`, `MOD`, `EQ`, etc., but also including brackets (both on the left side and right side of an assignment) and other special methods used by `PRINT`, `HELP`, and `SIZE`. The dot operator is automatically connected to the `getProperty` and `setProperty` methods of the class.
Another nice point is that GPULib will not require separate versions for pre-8.0 and post-8.0 versions of IDL. Just write a simple dummy `IDL_Object` class. This will allow the code to be compiled in versions of IDL before 8.0 and won't be found (because the real `IDL_Object` is part of IDL's core and found before any user routines) in versions 8.0+. Of course, only the old procedure or function interfaces are available in versions before 8.0. I'm much more likely to use operator overloading because I can provide extra features for IDL 8.0 users and fall back to a more verbose interface for those who have not upgraded yet.
If you have the tech preview handed out at the meeting or are just interested in some more examples of this, check out these [HDF5 classes](http://michaelgalloy.com/wp-content/uploads/2010/02/hdf5.zip) which make use of operator overloading. The end of the `mg_h5.pro` file has a main-level program which shows how to use the classes:
IDL> .run mg_h5
*Full disclosure: I work for Tech-X Corporation and have worked on the IDL bindings for GPULib.*