On 08/24/2015 05:30 AM, Markus Armbruster wrote:
>> We mentioned moving this into its own patch. In particular, I looked at
>> what it would take to allow anonymous structs for flat union types:
>>
>> { 'union': 'Flat', 'base': 'Base',
>> 'discriminator': 'type',
>> 'data': { 'branch1': {},
This one is particularly handy - it would avoid the need to create dummy
types like 'Abort' that exist solely to satisfy the current qapi grammar.
>> 'branch2': { 'integer': 'int' } } }
This one is a bit harder to justify, but may still be useful.
>
> We used to support inline structs in a few places, but dropped it
> (commit 6b5abc7). Do we really want to add them back in other places?
We dropped nested structs, not anonymous structs.
For comparison, here's an anonymous command struct:
{ 'command': 'foo', 'data': { 'i': 'int' } }
vs. the corresponding named version:
{ 'struct': 'Foo', 'data': { 'i': 'int' } }
{ 'command': 'foo', 'data': 'Foo' }
Where things would NOT be allowed due to our prohibition of nested
structs is:
{ 'union': 'Flat', 'base': 'Base', 'discriminator': 'type',
'data': { 'okay': 'str', 'bad': { 'i': 'int' } } }
>
> Both Abort and ChardevDummy exist only because you need a type to
> declare a simple union case. I'd like to explore cleaning up the
> convoluted union syntax first. If we then still have a need for empty
> structs, we can consider optimizing them.
And that's where my patches were headed - by allowing a dict instead of
a type name for the branches of a flat union, the syntax for flat unions
becomes simpler, and allows us to sanely represent a
"no-additional-members" variant without needing 'Abort' as an empty type.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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