libcamera: yaml_parser: Make default value templated in get()

This way the construction of the default value of type `T`
can be delayed until it is really needed, which is useful,
for example when `T == std::string` and the default value comes
from a string literal, as the default value string would always
be constructed otherwise, even if not needed.

Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/yaml_parser.h

@@ -179,10 +179,10 @@ public:
 #endif
 	std::optional<T> get() const;
 
-	template<typename T>
-	T get(const T &defaultValue) const
+	template<typename T, typename U>
+	T get(U &&defaultValue) const
 	{
-		return get<T>().value_or(defaultValue);
+		return get<T>().value_or(std::forward<U>(defaultValue));
 	}
 
 #ifndef __DOXYGEN__

src/libcamera/yaml_parser.cpp

@@ -104,7 +104,7 @@ std::size_t YamlObject::size() const
  */
 
 /**
- * \fn template<typename T> YamlObject::get<T>(const T &defaultValue) const
+ * \fn template<typename T, typename U> YamlObject::get<T>(U &&defaultValue) const
  * \brief Parse the YamlObject as a \a T value
  * \param[in] defaultValue The default value when failing to parse
  *