[IronPython] Decorators on classes

[Keith J. Farmer]

Grandfathering: Giving more consideration to retaining compatibility than it deserves. :)
 
Obviously, IronPython should prioritize compatibility with Py2.4, but for obvious reasons I limit that to seeing IP as a consumer of CPy, not the other way around.  On the other hand, IP must also be able to consume .NET, and .NET is increasingly making use of things the IP cannot yet express.  (I thought of another framework that attributes are used on -- WCF.  There are also XML serialization attributes.)
 
To that end, I think it would be worthwhile, for the purpose of .NET attributes, to have decorators or their analogues available to IronPython in the current stage of development.  That is, I think it should be that IronPython = CPy 2.4 + .NET Attributes + other .NET-isms expressed in a Pythonic way.

________________________________

From: users-bounces at lists.ironpython.com on behalf of Michael Foord
Sent: Mon 2/4/2008 11:53 AM
To: Discussion of IronPython
Subject: Re: [IronPython] Decorators on classes



Keith J. Farmer wrote:
> I've had no problems with not grandfathering in older APIs, and am quite happy to not grandfather in older syntax, either.
>  

What do you mean by 'grandfathering' in this context?

Michael

> 
> I agree that IronPython would have to be able to distinguish between CLR attributes and Python decorators, inasmuch as CLR attributes are a static part of the class/member definition.  But I don't think it's an insurmountable problem, and solving it in the DLR, actually, would be very useful.
> 
> I wouldn't expect that class authors would want to change the set of .NET attributes frequently if at all -- it doesn't match how they've been designed and how they've evolved, so creating the attributed base class once (and then having pythonic decorators coming in and out at will) seems like a reasonable approach to me.
>
> ________________________________
>
> From: users-bounces at lists.ironpython.com on behalf of Curt Hagenlocher
> Sent: Mon 2/4/2008 11:13 AM
> To: Discussion of IronPython
> Subject: Re: [IronPython] Decorators on classes
>
>
> Oh! I didn't realize that about 2.6.
> 
> There is indeed a big difference between a Python runtime decorator and a .NET compile time attribute; in fact, the similarities are superficial at best.
> 
> .NET attributes are totally static, so there's no way to modify a .NET class definition to add them.  The IronPython engine would have to recognize particular class-level Pythonic annotations and use that information to emit a new CLR class to represent the Python class.  It already emits CLR classes as needed to represent Python classes.  By "as needed", I mean that a specific CLR base class plus a specific set of CLR interfaces will uniquely determine a class to be emitted by IronPython.  This class is cached so that -- once generated -- any new Python class definition that matches this set of (CLR base class plus interfaces) will reuse the same CLR class definition.
> 
> What you'd have to change is to put the class-level attributes onto the generated CLR class, then change caching so that the key is (CLR base class plus interfaces plus attributes).  It's definitely doable, but raises intriguing questions about "purity".  And you'd also need to consider the impact on the larger DLR.
>
> Method-level attributes are an entirely different matter.
>
> On Feb 4, 2008 10:58 AM, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
>
>
>       Class decorators will be in Python 2.6 - but there is a big difference
>       between a Python runtime decorator and .NET compile time attributes. Is
>       it possible to attach attributes at runtime using the reflection API?
>      
>       Michael
>       http://www.manning.com/foord
>      
>
>       Keith J. Farmer wrote:
>       > Can I resurrect this forgotten soul?  http://www.codeplex.com/WorkItem/View.aspx?ProjectName=IronPython&WorkItemId=13583
>       >
>       > Having just finished working on LINQ to SQL, I'm convinced that future LINQ providers will be making heavy use of .NET attributes not just on properties, but on classes themselves.  Being able to express these attributes in IronPython is a tremendous bonus.  That there be one and only one way to express these is paramount.
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