valueDiff for arrays?

[Mark Waddingham]

On 2018-08-07 23:31, Mark Wieder via use-livecode wrote:
> On 08/07/2018 02:21 PM, Mark Waddingham via use-livecode wrote:
>> However, the engine treats arrays which have all integer (string) keys 
>> starting at one and are dense (i.e. the number of elements == max(all 
>> keys)) from ones that aren't.

There should have been a 'differently' in there.

> Not sure how to interpret that. If I create
> 
> repeat with i=1 to 10
>   put i into tArray[i]
> end repeat
> 
> to make a 'special' array and then
> delete variable tArray[3]
> 
> does that take it out of the 'special' category?

Yes - unless the array's first key is 1, and it then has all integer 
keys up to and including its number of elements  then it is not 
considered a sequence array.

i.e. [1], [3], [5] - not a sequence
      [2], [3], [4] - not a sequence
      [1], [2], [3] - a sequence

The specialness is quite restricted - however such arrays:

   1) are ordered when used with 'repeat for each element' *not* repeat 
for each key:

        repeat for each element tElement in tSeqArray
          ... tElement will first be [1], then [2], ... then [n] ...
        end repeat

   2) can be used as a sequence of keys to traverse in [] - e.g.

       put tArray[tSeqArray] == tArray[tSeqArray[1]]...[tSeqArray[2]]

   3) admit a more efficient representation in arrayEncode - they are 
encoded as 'sequences', so the engine does not emit the keys - instead 
it just emits a sequence of values [1], [2], ..., [n]... Which saves 
some space.

Warmest Regards,

Mark.

-- 
Mark Waddingham ~ mark at livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps