From 48c106429a197d9c35c30523d3f5c711f3137333 Mon Sep 17 00:00:00 2001
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Date: Wed, 27 Jul 2022 23:51:17 +0300
Subject: libcamera: base: utils: Provide defopt to simplify
std::optional::value_or() usage
The std::optional<T>::value_or(U &&default_value) function returns the
contained value if available, or default_value if the std::optional has
no value. If the desired default value is a default-constructed T, the
obvious option is to call std::optional<T>::value_or(T{}). This approach
has two drawbacks:
- The \a default_value T{} is constructed even if the std::optional
instance has a value, which impacts efficiency.
- The T{} default constructor needs to be spelled out explicitly in the
value_or() call, leading to long lines if the type is complex.
Introduce a defopt variable that solves these issues by providing a
value that can be passed to std::optional<T>::value_or() and get
implicitly converted to a default-constructed T.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
---
src/libcamera/base/utils.cpp | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
(limited to 'src')
diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp
index 6a307940..9cd6cb19 100644
--- a/src/libcamera/base/utils.cpp
+++ b/src/libcamera/base/utils.cpp
@@ -463,6 +463,27 @@ std::string toAscii(const std::string &str)
* \a b
*/
+/**
+ * \var defopt
+ * \brief Constant used with std::optional::value_or() to create a
+ * default-constructed object
+ *
+ * The std::optional<T>::value_or(U &&default_value) function returns the
+ * contained value if available, or \a default_value if the std::optional has no
+ * value. If the desired default value is a default-constructed T, the obvious
+ * option is to call std::optional<T>::value_or(T{}). This approach has two
+ * drawbacks:
+ *
+ * * The \a default_value T{} is constructed even if the std::optional instance
+ * has a value, which impacts efficiency.
+ * * The T{} default constructor needs to be spelled out explicitly in the
+ * value_or() call, leading to long lines if the type is complex.
+ *
+ * The defopt variable solves these issues by providing a value that can be
+ * passed to std::optional<T>::value_or() and get implicitly converted to a
+ * default-constructed T.
+ */
+
} /* namespace utils */
#ifndef __DOXYGEN__
--
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