RE: Why only scalar arrays?

[Malitsky, N. D <mal...@bn...>]

For me, it identifies two conceptual problems.

1.PvData is overwhelmed with the server and client requirements. 
For me, PvStructure has to address (only) a single task: a dynamic container with a general (narrow) fast interface. 
This container can be reused or/and extended with the additional features in the different environments. 

2.Array of structures should have a single element type (at least, according to the present programming methodology). 
Again, I would consider PvStructure as a C fixed structure, but a pointer to the C++ class. 

Nikolay



-----Original Message-----
From: Benjamin Franksen [mailto:ben...@be...]
Sent: Mon 4/19/2010 9:35 AM
To: epi...@li...
Subject: Re: Why only scalar arrays?
 
On Monday 19 April 2010, Marty Kraimer wrote:
> I am answering this message before the previous two message you sent
> because it is easier to answer quickly.

I thought so ;-)

> Earlier versions of javaIOC did allow arrays of structures and arrays of
> arrays. The support was removed because it was causing major problems. A
> simple example will show the problem:
> 
> Suppose we have the following structure of fields:
> 
> top
>     xxx which is an array of structures
>         [0]
>             value
>             ...
>        [1]
>             value
>             ...
> 
> A client was allowed  to connect to
>  top.xxx[1].value
> 
> Also each element of xxx could have a completely different Structure
> defining the set of fields in the structure.

I would have expected them to be (=have to be) all the same type of 
structure. Looks as if the new implementation you allude to below seems to 
do it that way.

> Now what happens if  structure top[1] is replaced by another structure
> or the length of top is set to 1?
> 
> This was really a mess.  All kinds of problems arose.

I can imagine that! But... I wonder why this is only a problem with arrays. 
For instance, consider this

top
    xxx  which is a structure
        yyy  which is another (sub-) structure

Now, what happens if structure yyy is replaced by another structure or just 
gets removed from structure xxx? Isn't this exactly the same situation?

Cheers
Ben

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