Re: [EXTERNAL] Re: Change PVA structure dynamically during IOC operation

[bob dalesio via Tech-talk <tech-talk@aps.anl.gov>]

Any's are fraught with cost. I have never thought they were a good idea.

Bob

On Wed, Sep 28, 2022, 2:38 PM Kasemir, Kay via Tech-talk <tech-talk@aps.anl.gov> wrote:

You're right, I missed the Any type.

It does encode the structure description with each update, so missing out the efficiency usually offered in the protocol.

Yes, union would be better. It describes all options once, then sends updates with just the index of the option that's being used.

---

From: Andrew Johnson <anj@anl.gov>

PVA does support unions though, and an "any" type, so assuming you can design all the versions of the structure that you will need up front (and that the pvxs implementation supports them) you should be able to use them to make changes to your PVA structure without having to withdraw and re-add the PV. I believe a union will be more efficient than using an "any".