[elephant-devel] Re: Array slots

[Ian Eslick]

Alex is exactly right, as pointed out by the docs.  set-valued slots  
partially solve this annoyance with persistent collections stored in  
slots, but they are unordered.

Unfortunately aref is not a generic function so you'd have to play  
package naming games to hijack it which I abhor.  I'm open to  
suggestions on ways to handle such an idiom, but nothing has come to  
mind yet.  A macro to create slot accessors that do all the  
bookkeeping automatically might be useful as an option for users.

Ian

On Apr 29, 2008, at 3:24 PM, Alex Mizrahi wrote:

> LPP> (32): (setf (aref (slot-value sch 'a) 2) 1)
> LPP> 1
>
> LPP> (33): (slot-value sch 'a)
> LPP> #(0 0 0 0)
>
> how do you thik it is supposed to work?
> to my knowledge, elephant does not hijack (setf aref), so (setf  
> aref) just
> modifies a temporary array returned by a slot read.
> db is written _only_ on (setf slot-value), if you do not explicitly  
> write to
> slot, value in database won't be updated.
> it seems this stuff is in documentation:
>
> ----
> 2.7 Persistent collections
>
> The remaining problem outlined in the section on Serialization is that
> operations which mutate collection types do not have persistent side
> effects. We have solved this problem for objects, but not for  
> collections
> such as as arrays, hashes or lists. Elephant provides two solutions  
> to this
> problem: the pset and btree classes. Each provides persistent  
> addition,
> deletion and mutation of elements, but the pset is a simple data  
> structure
> that may be more efficient in memory and time than the more general  
> btree.
> ----
>
>
>
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