[PATCH] libcamera: yaml-parser: Differentiate between empty and empty string

[Stefan Klug]

Hi Barnabás,

On Tue, Sep 17, 2024 at 01:45:13PM +0000, Barnabás Pőcze wrote:
> Hi
> 
> 
> 2024. szeptember 17., kedd 00:28 keltezéssel, Stefan Klug <stefan.klug at ideasonboard.com> írta:
> 
> > When accessing a nonexistent key on a dict the YamlObject returns an
> > empty element. This element can happily be casted to a string which is
> > unexpected. For example the following statement:
> > yamlDict["nonexistant"].get<string>("default") is expected to return
> > "default" but actually returns "". Fix this by introducing a empty type
> > to distinguish between an empty YamlObject and a YamlObject of type
> > value containing an empty string. For completeness add an isEmpty()
> > function to be able to test for that type.
> > 
> > Signed-off-by: Stefan Klug <stefan.klug at ideasonboard.com>
> > ---
> >  include/libcamera/internal/yaml_parser.h |  5 +++++
> >  src/libcamera/yaml_parser.cpp            | 20 ++++++++++++++------
> >  test/yaml-parser.cpp                     |  6 ++++++
> >  3 files changed, 25 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/yaml_parser.h b/include/libcamera/internal/yaml_parser.h
> > index 16708e488d88..33c3a96fed47 100644
> > --- a/include/libcamera/internal/yaml_parser.h
> > +++ b/include/libcamera/internal/yaml_parser.h
> > @@ -159,6 +159,10 @@ public:
> >  	{
> >  		return type_ == Type::Dictionary;
> >  	}
> > +	bool isEmpty() const
> > +	{
> > +		return type_ == Type::Empty;
> > +	}
> 
> I think `constexpr explicit operator bool() const` would be a good addition as well.
> Then you can just do e.g.
> 
>   if (auto y = x["something"]) {
>     // ...
>   }

Thanks for the suggestion. I'll add that. One question though. Why the
constexpr? I can't come up with a practical case were that can be
resolved at compiletime.

Best regards,
Stefan

> 
> 
> > 
> >  	std::size_t size() const;
> > 
> > @@ -212,6 +216,7 @@ private:
> >  		Dictionary,
> >  		List,
> >  		Value,
> > +		Empty,
> >  	};
> > [...]
> 
> 
> Regards,
> Barnabás Pőcze