From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH RFC 4/9] libxl_internal: introduce
 libxl__json_object_is_{null, number, double}
Date: Tue, 15 Apr 2014 10:29:56 +0100
Message-ID: <20140415092956.GI3635@zion.uk.xensource.com>
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: ian.jackson@eu.citrix.com, Wei Liu <wei.liu2@citrix.com>, xen-devel@lists.xen.org
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On Mon, Apr 14, 2014 at 06:04:27PM +0100, Ian Campbell wrote:
> On Thu, 2014-04-10 at 16:40 +0100, Wei Liu wrote:
> > ... which return true if json object is valid and of type
> > JSON_{NULL,NUMBER,DOUBLE}.
> > 
> > Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> 
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
> 
> But... 
> > +static inline bool libxl__json_object_is_null(const libxl__json_object *o)
> > +{
> > +    return o != NULL && o->type == JSON_NULL;
> 
> Shouldn't these (new and existing) use the bit field stuff you just
> introduced?
> 

No, this tests on the exact type, because a JSON object only has one
type.

The previous bit-field patch is for a different purpose. When you try to
parse a libxl_FOO field from a JSON object, the JSON object can be of
different type. For example, (key, value) pair in key_value_list type,
the generated key in JSON object is a string, but the value can be a
string or null depending on the input to JSON object generator
(libxl__object_to_json).

The bit-field patch works like this, say, if we want to parse that (key,
value) pair, we will certainly expect (JSON_STRING | JSON_NULL) in

    x = libxl__json_map_get("value", o, JSON_STRING|JSON_NULL);

but later in the actual function that parses x, x can be either
JSON_STRING or JSON_NULL; it cannot be of two types at the same time.

Wei.

> Ian.