Re: draft-ietf-appsawg-json-pointer-07 - array index for end ofarray

[Mark Nottingham <[e-mail]>]

David,

This was discussed in the Working Group, but it wasn't felt that the added complexity was worth it; there's a strong feeling that this spec should be as simple as possible.

Cheers,


On 15/12/2012, at 4:54 AM, David J. Biesack <[e-mail]> wrote:

> 
> I originally posted this in a "Re: Last Call: <draft-ietf-appsawg-json-patch-08.txt> (JSON Patch) to Proposed Standard" thread
> but now I've read draft-ietf-appsawg-json-pointer-07 and have changed that suggestion to reflect draft-ietf-appsawg-json-pointer-07
> 
> Suggestion: allow negative numbers to indicate a position counted from the end of the array instead "array/-".
> 
> For example, a/-1 to point to the last item in an array (length > 0), -2 to point to the penultimate item, and so on. 
> The notation -i is an alias for (array.length - i)
> 
> It is an error if |i| > array length.
> 
> For the json-patch "add" operation, use 
> 
>   { "op" : "add", "path" : "...array/-1", "value" : value } 
> 
> to append to the end, "...array/-2" to insert before the last item, and so on.
> The "path" is the path that the item will be addressed by after inserting it.
> I.e. after appending to an array of length l at j < 0, the item will be at the zero-based index (l + 1) + j. 
> 
> E.g. given the document with an array of length 4:
> 
> { "a" : [ 0, 1, 2, 3, ] }
> 
> then 
> 
> { "op" : "add", "path" : "/a/-1", "value" : 99 }
> 
> yields
> 
> { "a" : [ 0, 1, 2, 3, 99] }
> 
> i.e. 99 is found at (4 + 1) -1 == 4
> 
> 
> { "op" : "add", "path" : "/a/-2", "value" : 99}
> 
> yields
> 
> { "a" : [ 0, 1, 2, 99, 3] }
> 
> i.e. 99 is found at (4 + 1) -2 == 3
> 
> and finally
> 
> { "op" : "add", "path" : "/a/-5", "value" : 99 }
> 
> yields
> 
> { "a" : [ 99, 0, 1, 2, 3] }
> 
> i.e. 99 is found at (4 + 1) -5 == 0
> 
> -- 
> David J. Biesack | Principal API Architect, SAS | @davidbiesack | 919-531-7771 | www.sas.com
> 

--
Mark Nottingham   http://www.mnot.net/