Adding optional UUID to layouts

[Ty Young]

On 3/24/20 9:18 AM, Maurizio Cimadamore wrote:
>
> On 24/03/2020 12:14, Ty Young wrote:
>> MemoryLayout.ofValueBits(1, 
>> ByteOrder.nativeOrder()).withName("bool").withUuid(UUID.randomUUID()); 
>
> What I'm saying is that withName is just a withAttribute(NAME, 
> "bool"), where an attribute can be any Java object that implements the 
> Constable interface. So it might be possible to do something like
>
> layout.withAttribute("library", "OpenGL")
>
> and that will make all layouts generated in a given extraction run 
> 'unique' (since equals() and hashCode() take attributes into account).
>
> See:
>
> https://git.openjdk.java.net/panama-foreign/pull/64
>
> Which Jorn has timely submitted :-)


No kidding. It's almost creepy how on top of things like this you all 
are. I wish I knew these things were being worked on beforehand so I 
don't end up bothering you all so much.


Many thanks.


>
> In general - we're NOT going to add a UUID to add layouts just because 
> in some cases it feels it's handy to have one. But that's why the 
> layout attribute machinery comes in place - to add extra side-info to 
> the layout w/o necessarily making the API more complex with things 
> that most users won't even care about.
>
> So, your question can be rephrased as: can jextract please attach a 
> standard layout attribute to all the layout it emits during a single 
> run, so that layouts from library A cannot be confused with layouts 
> coming from library B?
>
> Right now we haven't discussed anything in that direction - the new 
> API (see above PR) makes it possible; another possibility is that your 
> API could be in charge of the decorating process (e.g. if your API 
> only works with layouts which have an 'uuid' then have a function 
> which takes a layout and returns a new layout with the desired uuid 
> embedded as a layout attribute).


Right, good idea.


A question here, if you don't mind, is does the JVM have memory 
optimizations for things like ValueLayout? Or is ValueLayout manually 
optimized by passing object instances through the constructor?


>
> Maurizio
>