libcamera: yaml_parser: Take string keys in `std::string_view`

In many cases a static string literal is used as key. Thus
having the argument type be `const std::string&` is suboptimal
since an `std::string` object needs to be constructed before
the call.

C++17 introduced `std::string_view`, using which the call
can be done with less overhead, as the `std::string_view`
is non-owning and may be passed in registers entirely.

So make `YamlObject::{contains,operator[]}` take the string keys
in `std::string_view`s.

Unfortunately, that is not sufficient yet, because `std::map::find()`
takes an reference to `const key_type`, which would be `const std::string&`
in the case of `YamlParser`. However, with a transparent comparator
such as `std::less<>` `std::map::find()` is able to accept any
object as the argument, and it forwards it to the comparator.

So make `YamlParser::dictionary_` use `std::less<>` as the comparator
to enable the use of `std::map::find()` with any type of argument.

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

1 files changed, 4 insertions, 3 deletions

diff --git a/include/libcamera/internal/yaml_parser.h b/include/libcamera/internal/yaml_parser.h
index 6211ff4a..de452844 100644
--- a/include/libcamera/internal/yaml_parser.h
+++ b/include/libcamera/internal/yaml_parser.h
@@ -12,6 +12,7 @@
 #include <optional>
 #include <stdint.h>
 #include <string>
+#include <string_view>
 #include <vector>
 
 #include <libcamera/base/class.h>
@@ -206,8 +207,8 @@ public:
 
 	const YamlObject &operator[](std::size_t index) const;
 
-	bool contains(const std::string &key) const;
-	const YamlObject &operator[](const std::string &key) const;
+	bool contains(std::string_view key) const;
+	const YamlObject &operator[](std::string_view key) const;
 
 private:
 	LIBCAMERA_DISABLE_COPY_AND_MOVE(YamlObject)
@@ -232,7 +233,7 @@ private:
 
 	std::string value_;
 	Container list_;
-	std::map<std::string, YamlObject *> dictionary_;
+	std::map<std::string, YamlObject *, std::less<>> dictionary_;
 };
 
 class YamlParser final