Improving inspect on class objects

[Patrick R. Michaud]

On Mon, Jan 05, 2009 at 01:09:07AM -0800, Allison Randal wrote:
> Okay, (2) is taken care of with 'get_attr_*'/'set_attr_*'. (1) works  
> fine as a clone (not modifying, just reading), but creating a clone of  
> the attribute metadata every time you instantiate a new object is way  
> too expensive.
>
> I suggest exploring what we need out of this a little further. Again the  
> 'inspect' vtable function isn't really right for it. It might be a class  
> method.

There's already class method for this -- 'attributes'.  In fact, that's
what Rakudo is actually using to get its list of attributes, but at 
present 'attributes' just forwards to inspect_str (which is what
brought up the original post about inspect_str).

A related question to all of this is whether the hashes returned
by get_attr_* are also shallow-clones of the attribute metadata hash
for any given attribute.  If we return an attribute's metadata hash
directly, then the caller can use it to modify the attribute's
metadata (but not the overall hash of attributes).  If we want to
prevent even this level of modification by the caller, then get_attr_*
needs to return a shallow clone of the attribute's metadata.  In
this case inspect_str and attributes would return a hash of these
shallow clones.

Personally, I find all of this cloning-to-prevent-modification a bit
troubling.  I'd rather simply say "modifying the hashes returned
from 'attributes' and get_attr_* is illegal" and not have callers
that simply want to obtain attribute metadata incur the repeated
cloning expense to do so.  This is doubly-true since the Class PMC 
doesn't (yet?) actually use any of the attribute metadata hash entries 
for its own purposes -- at the moment the per-attribute metadata 
hashes seem to exist solely for the benefit of the caller.
If Parrot is going to make using those metadata hashes expensive,
then from a HLL perspective I think I'd rather just manage my own
attribute metadata entirely outside of the Class PMC.

Anyway, let me know which approach you want Parrot to take
and I'll make it happen.

Pm