Re: [Qemu-devel] [PATCH v14 02/21] qdict: implement a qdict_crumple method for un-flattening a dict

[Markus Armbruster]

"Daniel P. Berrange" <address@hidden> writes:

> On Tue, Oct 18, 2016 at 04:32:13PM +0200, Markus Armbruster wrote:
>> "Daniel P. Berrange" <address@hidden> writes:
>> 
>> > The qdict_flatten() method will take a dict whose elements are
>> > further nested dicts/lists and flatten them by concatenating
>> > keys.
>> >
>> > The qdict_crumple() method aims to do the reverse, taking a flat
>> > qdict, and turning it into a set of nested dicts/lists. It will
>> > apply nesting based on the key name, with a '.' indicating a
>> > new level in the hierarchy. If the keys in the nested structure
>> > are all numeric, it will create a list, otherwise it will create
>> > a dict.
>> >
>> > If the keys are a mixture of numeric and non-numeric, or the
>> > numeric keys are not in strictly ascending order, an error will
>> > be reported.
>> >
>> > As an example, a flat dict containing
>> >
>> >  {
>> >    'foo.0.bar': 'one',
>> >    'foo.0.wizz': '1',
>> >    'foo.1.bar': 'two',
>> >    'foo.1.wizz': '2'
>> >  }
>> >
>> > will get turned into a dict with one element 'foo' whose
>> > value is a list. The list elements will each in turn be
>> > dicts.
>> >
>> >  {
>> >    'foo': [
>> >      { 'bar': 'one', 'wizz': '1' },
>> >      { 'bar': 'two', 'wizz': '2' }
>> >    ],
>> >  }
>> >
>> > If the key is intended to contain a literal '.', then it must
>> > be escaped as '..'. ie a flat dict
>> >
>> >   {
>> >      'foo..bar': 'wizz',
>> >      'bar.foo..bar': 'eek',
>> >      'bar.hello': 'world'
>> >   }
>> >
>> > Will end up as
>> >
>> >   {
>> >      'foo.bar': 'wizz',
>> >      'bar': {
>> >         'foo.bar': 'eek',
>> >         'hello': 'world'
>> >      }
>> >   }
>> >
>> > The intent of this function is that it allows a set of QemuOpts
>> > to be turned into a nested data structure that mirrors the nesting
>> > used when the same object is defined over QMP.
>> >
>> > Reviewed-by: Eric Blake <address@hidden>
>> > Reviewed-by: Kevin Wolf <address@hidden>
>> > Reviewed-by: Marc-André Lureau <address@hidden>
>> > Signed-off-by: Daniel P. Berrange <address@hidden>
>> > ---
>> >  include/qapi/qmp/qdict.h |   1 +
>> >  qobject/qdict.c          | 289 
>> > +++++++++++++++++++++++++++++++++++++++++++++++
>> >  tests/check-qdict.c      | 261 ++++++++++++++++++++++++++++++++++++++++++
>> >  3 files changed, 551 insertions(+)
>> >
>> > diff --git a/include/qapi/qmp/qdict.h b/include/qapi/qmp/qdict.h
>> > index 71b8eb0..e0d24e1 100644
>> > --- a/include/qapi/qmp/qdict.h
>> > +++ b/include/qapi/qmp/qdict.h
>> > @@ -73,6 +73,7 @@ void qdict_flatten(QDict *qdict);
>> >  void qdict_extract_subqdict(QDict *src, QDict **dst, const char *start);
>> >  void qdict_array_split(QDict *src, QList **dst);
>> >  int qdict_array_entries(QDict *src, const char *subqdict);
>> > +QObject *qdict_crumple(const QDict *src, bool recursive, Error **errp);
>> >  
>> >  void qdict_join(QDict *dest, QDict *src, bool overwrite);
>> >  
>> > diff --git a/qobject/qdict.c b/qobject/qdict.c
>> > index 60f158c..c38e90e 100644
>> > --- a/qobject/qdict.c
>> > +++ b/qobject/qdict.c
>> [...]
>> > +/**
>> > + * qdict_crumple:
>> > + * @src: the original flat dictionary (only scalar values) to crumple
>> > + * @recursive: true to recursively crumple nested dictionaries
>> 
>> Is recursive=false used outside tests in this series?
>
> No, its not used.
>
> It was suggested in a way earlier version by Max, but not sure if his
> code uses it or not.

In general, I prefer features to be added right before they're used, and
I really dislike adding features "just in case".  YAGNI.

Max, do you actually need this one?  If yes, please explain your use
case.