libcamera: yaml_parser: Replace ok flag to get() with std::optional

The YamlObject::get() function takes a default value and an optional
bool ok flag to handle parsing errors. This ad-hoc mechanism complicates
error handling in callers.

A better API is possible by dropping the default value and ok flag and
returning an std::optional. Not only does it simplify the calls, it also
lets callers handle errors through the standard std::optional class
instead of the current ad-hoc mechanism.

Provide a get() wrapper around std::optional::value_or() to further
simplify callers that don't need any specific error handling.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Naushir Patuck <naush@raspberrypi.com>
Tested-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/internal/yaml_parser.h

@@ -9,6 +9,7 @@
 
 #include <iterator>
 #include <map>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -165,7 +166,13 @@ public:
 #else
 	template<typename T>
 #endif
-	T get(const T &defaultValue, bool *ok = nullptr) const;
+	std::optional<T> get() const;
+
+	template<typename T>
+	T get(const T &defaultValue) const
+	{
+		return get<T>().value_or(defaultValue);
+	}
 
 	DictAdapter asDict() const { return DictAdapter{ dictionary_ }; }
 	ListAdapter asList() const { return ListAdapter{ list_ }; }