[{"id":24203,"web_url":"https://patchwork.libcamera.org/comment/24203/","msgid":"","date":"2022-07-28T06:04:23","subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","submitter":{"id":86,"url":"https://patchwork.libcamera.org/api/people/86/","name":"Umang Jain","email":"umang.jain@ideasonboard.com"},"content":"Hi Laurent,\n\nThank you for the patch.\n\nOn 7/28/22 03:51, Laurent Pinchart via libcamera-devel wrote:\n> The std::optional::value_or(U &&default_value) function returns the\n> contained value if available, or \\a default_value if the std::optional\n> has no value. If the desired default value is a default-constructed T,\n> the obvious option is to call std::optional::value_or(T{}). This\n> approach has two drawbacks:\n>\n> - The \\a default_value T{} is constructed even if the std::optional\n> instance has a value, which impacts efficiency.\n> - The T{} default constructor needs to be spelled out explicitly in the\n> value_or() call, leading to long lines if the type is complex.\n>\n> Introduce a defopt variable that solves these issues by providing a\n> value that can be passed to std::optional::value_or() and get\n> implicitly converted to a default-constructed T.\n>\n> Signed-off-by: Laurent Pinchart \n\n\nReviewed-by: Umang Jain \n\n> ---\n> include/libcamera/base/utils.h | 14 +++++++++\n> src/libcamera/base/utils.cpp | 21 +++++++++++++\n> test/utils.cpp | 54 ++++++++++++++++++++++++++++++++++\n> 3 files changed, 89 insertions(+)\n>\n> diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h\n> index cfff05836de7..889bb4a2270e 100644\n> --- a/include/libcamera/base/utils.h\n> +++ b/include/libcamera/base/utils.h\n> @@ -361,6 +361,20 @@ decltype(auto) abs_diff(const T &a, const T &b)\n> \t\treturn a - b;\n> }\n> \n> +namespace details {\n> +\n> +struct defopt_t {\n> +\ttemplate\n> +\toperator T() const\n> +\t{\n> +\t\treturn T{};\n> +\t}\n> +};\n> +\n> +} /* namespace details */\n> +\n> +constexpr details::defopt_t defopt;\n> +\n> } /* namespace utils */\n> \n> #ifndef __DOXYGEN__\n> diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp\n> index 6a307940448e..9cd6cb197243 100644\n> --- a/src/libcamera/base/utils.cpp\n> +++ b/src/libcamera/base/utils.cpp\n> @@ -463,6 +463,27 @@ std::string toAscii(const std::string &str)\n> * \\a b\n> */\n> \n> +/**\n> + * \\var defopt\n> + * \\brief Constant used with std::optional::value_or() to create a\n> + * default-constructed object\n> + *\n> + * The std::optional::value_or(U &&default_value) function returns the\n> + * contained value if available, or \\a default_value if the std::optional has no\n> + * value. If the desired default value is a default-constructed T, the obvious\n> + * option is to call std::optional::value_or(T{}). This approach has two\n> + * drawbacks:\n> + *\n> + * * The \\a default_value T{} is constructed even if the std::optional instance\n> + * has a value, which impacts efficiency.\n> + * * The T{} default constructor needs to be spelled out explicitly in the\n> + * value_or() call, leading to long lines if the type is complex.\n> + *\n> + * The defopt variable solves these issues by providing a value that can be\n> + * passed to std::optional::value_or() and get implicitly converted to a\n> + * default-constructed T.\n> + */\n> +\n> } /* namespace utils */\n> \n> #ifndef __DOXYGEN__\n> diff --git a/test/utils.cpp b/test/utils.cpp\n> index d65467b5102c..129807a63ec6 100644\n> --- a/test/utils.cpp\n> +++ b/test/utils.cpp\n> @@ -7,6 +7,7 @@\n> \n> #include \n> #include \n> +#include \n> #include \n> #include \n> #include \n> @@ -169,6 +170,55 @@ protected:\n> \t\treturn TestPass;\n> \t}\n> \n> +\tint testDefopt()\n> +\t{\n> +\t\tstatic bool defaultConstructed = false;\n> +\n> +\t\tstruct ValueType {\n> +\t\t\tValueType()\n> +\t\t\t\t: value_(-1)\n> +\t\t\t{\n> +\t\t\t\tdefaultConstructed = true;\n> +\t\t\t}\n> +\n> +\t\t\tValueType(int value)\n> +\t\t\t\t: value_(value)\n> +\t\t\t{\n> +\t\t\t}\n> +\n> +\t\t\tint value_;\n> +\t\t};\n> +\n> +\t\t/*\n> +\t\t * Test that utils::defopt doesn't cause default-construction\n> +\t\t * of a ValueType instance when value_or(utils::defopt) is\n> +\t\t * called on a std::optional that has a value.\n> +\t\t */\n> +\t\tstd::optional opt = ValueType(0);\n> +\t\tValueType value = opt.value_or(utils::defopt);\n> +\n> +\t\tif (defaultConstructed || value.value_ != 0) {\n> +\t\t\tstd::cerr << \"utils::defopt didn't prevent default construction\"\n> +\t\t\t\t << std::endl;\n> +\t\t\treturn TestFail;\n> +\t\t}\n> +\n> +\t\t/*\n> +\t\t * Then test that the ValueType is correctly default-constructed\n> +\t\t * when the std::optional has no value.\n> +\t\t */\n> +\t\topt = std::nullopt;\n> +\t\tvalue = opt.value_or(utils::defopt);\n> +\n> +\t\tif (!defaultConstructed || value.value_ != -1) {\n> +\t\t\tstd::cerr << \"utils::defopt didn't cause default construction\"\n> +\t\t\t\t << std::endl;\n> +\t\t\treturn TestFail;\n> +\t\t}\n> +\n> +\t\treturn TestPass;\n> +\t}\n> +\n> \tint run()\n> \t{\n> \t\t/* utils::hex() test. */\n> @@ -281,6 +331,10 @@ protected:\n> \t\tif (testDuration() != TestPass)\n> \t\t\treturn TestFail;\n> \n> +\t\t/* utils::defopt test. */\n> +\t\tif (testDefopt() != TestPass)\n> +\t\t\treturn TestFail;\n> +\n> \t\treturn TestPass;\n> \t}\n> };","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 42CA5BE173\n\tfor ;\n\tThu, 28 Jul 2022 06:04:32 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 7BA0563311;\n\tThu, 28 Jul 2022 08:04:31 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id D7D67603E7\n\tfor ;\n\tThu, 28 Jul 2022 08:04:29 +0200 (CEST)","from [IPV6:2401:4900:1f3e:f7a:bc8f:12ed:b45f:c35d] (unknown\n\t[IPv6:2401:4900:1f3e:f7a:bc8f:12ed:b45f:c35d])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id AB2E78AF;\n\tThu, 28 Jul 2022 08:04:28 +0200 (CEST)"],"DKIM-Signature":["v=1; 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dkim=pass (1024-bit key; \n\tunprotected) header.d=ideasonboard.com\n\theader.i=@ideasonboard.com\n\theader.b=\"IBrdFuzz\"; dkim-atps=neutral","Message-ID":"","Date":"Thu, 28 Jul 2022 11:34:23 +0530","MIME-Version":"1.0","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101\n\tThunderbird/91.4.1","Content-Language":"en-US","To":"Laurent Pinchart ,\n\tlibcamera-devel@lists.libcamera.org","References":"<20220727222149.30627-1-laurent.pinchart@ideasonboard.com>\n\t<20220727222149.30627-2-laurent.pinchart@ideasonboard.com>","In-Reply-To":"<20220727222149.30627-2-laurent.pinchart@ideasonboard.com>","Content-Type":"text/plain; charset=UTF-8; format=flowed","Content-Transfer-Encoding":"7bit","Subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","From":"Umang Jain via libcamera-devel ","Reply-To":"Umang Jain ","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":24204,"web_url":"https://patchwork.libcamera.org/comment/24204/","msgid":"<20220728064705.3pxw7ndxo3dgia7u@uno.localdomain>","date":"2022-07-28T06:47:05","subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","submitter":{"id":3,"url":"https://patchwork.libcamera.org/api/people/3/","name":"Jacopo Mondi","email":"jacopo@jmondi.org"},"content":"Hi Laurent\n\nOn Thu, Jul 28, 2022 at 01:21:41AM +0300, Laurent Pinchart via libcamera-devel wrote:\n> The std::optional::value_or(U &&default_value) function returns the\n> contained value if available, or \\a default_value if the std::optional\n\nAre the \\a in the commit message intended ?\n\n> has no value. If the desired default value is a default-constructed T,\n> the obvious option is to call std::optional::value_or(T{}). This\n> approach has two drawbacks:\n>\n> - The \\a default_value T{} is constructed even if the std::optional\n> instance has a value, which impacts efficiency.\n> - The T{} default constructor needs to be spelled out explicitly in the\n> value_or() call, leading to long lines if the type is complex.\n>\n> Introduce a defopt variable that solves these issues by providing a\n> value that can be passed to std::optional::value_or() and get\n> implicitly converted to a default-constructed T.\n>\n> Signed-off-by: Laurent Pinchart \n> ---\n> include/libcamera/base/utils.h | 14 +++++++++\n> src/libcamera/base/utils.cpp | 21 +++++++++++++\n> test/utils.cpp | 54 ++++++++++++++++++++++++++++++++++\n> 3 files changed, 89 insertions(+)\n>\n> diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h\n> index cfff05836de7..889bb4a2270e 100644\n> --- a/include/libcamera/base/utils.h\n> +++ b/include/libcamera/base/utils.h\n> @@ -361,6 +361,20 @@ decltype(auto) abs_diff(const T &a, const T &b)\n> \t\treturn a - b;\n> }\n>\n> +namespace details {\n> +\n> +struct defopt_t {\n> +\ttemplate\n> +\toperator T() const\n> +\t{\n> +\t\treturn T{};\n> +\t}\n> +};\n> +\n> +} /* namespace details */\n> +\n> +constexpr details::defopt_t defopt;\n> +\n\nClever! this indeed explains how it works:\n\ntemplate< class U >\nconstexpr T value_or( U&& default_value ) const&;\n\nEquivalent to bool(*this) ? **this : static_cast(std::forward(default_value))\n\n\nReviewed-by: Jacopo Mondi \n\nThanks\n j\n\n> } /* namespace utils */\n>\n> #ifndef __DOXYGEN__\n> diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp\n> index 6a307940448e..9cd6cb197243 100644\n> --- a/src/libcamera/base/utils.cpp\n> +++ b/src/libcamera/base/utils.cpp\n> @@ -463,6 +463,27 @@ std::string toAscii(const std::string &str)\n> * \\a b\n> */\n>\n> +/**\n> + * \\var defopt\n> + * \\brief Constant used with std::optional::value_or() to create a\n> + * default-constructed object\n> + *\n> + * The std::optional::value_or(U &&default_value) function returns the\n> + * contained value if available, or \\a default_value if the std::optional has no\n> + * value. If the desired default value is a default-constructed T, the obvious\n> + * option is to call std::optional::value_or(T{}). This approach has two\n> + * drawbacks:\n> + *\n> + * * The \\a default_value T{} is constructed even if the std::optional instance\n> + * has a value, which impacts efficiency.\n> + * * The T{} default constructor needs to be spelled out explicitly in the\n> + * value_or() call, leading to long lines if the type is complex.\n> + *\n> + * The defopt variable solves these issues by providing a value that can be\n> + * passed to std::optional::value_or() and get implicitly converted to a\n> + * default-constructed T.\n> + */\n> +\n> } /* namespace utils */\n>\n> #ifndef __DOXYGEN__\n> diff --git a/test/utils.cpp b/test/utils.cpp\n> index d65467b5102c..129807a63ec6 100644\n> --- a/test/utils.cpp\n> +++ b/test/utils.cpp\n> @@ -7,6 +7,7 @@\n>\n> #include \n> #include \n> +#include \n> #include \n> #include \n> #include \n> @@ -169,6 +170,55 @@ protected:\n> \t\treturn TestPass;\n> \t}\n>\n> +\tint testDefopt()\n> +\t{\n> +\t\tstatic bool defaultConstructed = false;\n> +\n> +\t\tstruct ValueType {\n> +\t\t\tValueType()\n> +\t\t\t\t: value_(-1)\n> +\t\t\t{\n> +\t\t\t\tdefaultConstructed = true;\n> +\t\t\t}\n> +\n> +\t\t\tValueType(int value)\n> +\t\t\t\t: value_(value)\n> +\t\t\t{\n> +\t\t\t}\n> +\n> +\t\t\tint value_;\n> +\t\t};\n> +\n> +\t\t/*\n> +\t\t * Test that utils::defopt doesn't cause default-construction\n> +\t\t * of a ValueType instance when value_or(utils::defopt) is\n> +\t\t * called on a std::optional that has a value.\n> +\t\t */\n> +\t\tstd::optional opt = ValueType(0);\n> +\t\tValueType value = opt.value_or(utils::defopt);\n> +\n> +\t\tif (defaultConstructed || value.value_ != 0) {\n> +\t\t\tstd::cerr << \"utils::defopt didn't prevent default construction\"\n> +\t\t\t\t << std::endl;\n> +\t\t\treturn TestFail;\n> +\t\t}\n> +\n> +\t\t/*\n> +\t\t * Then test that the ValueType is correctly default-constructed\n> +\t\t * when the std::optional has no value.\n> +\t\t */\n> +\t\topt = std::nullopt;\n> +\t\tvalue = opt.value_or(utils::defopt);\n> +\n> +\t\tif (!defaultConstructed || value.value_ != -1) {\n> +\t\t\tstd::cerr << \"utils::defopt didn't cause default construction\"\n> +\t\t\t\t << std::endl;\n> +\t\t\treturn TestFail;\n> +\t\t}\n> +\n> +\t\treturn TestPass;\n> +\t}\n> +\n> \tint run()\n> \t{\n> \t\t/* utils::hex() test. */\n> @@ -281,6 +331,10 @@ protected:\n> \t\tif (testDuration() != TestPass)\n> \t\t\treturn TestFail;\n>\n> +\t\t/* utils::defopt test. */\n> +\t\tif (testDefopt() != TestPass)\n> +\t\t\treturn TestFail;\n> +\n> \t\treturn TestPass;\n> \t}\n> };\n> --\n> Regards,\n>\n> Laurent Pinchart\n>","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id CC0ECC3275\n\tfor ;\n\tThu, 28 Jul 2022 06:47:14 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 2B36363311;\n\tThu, 28 Jul 2022 08:47:14 +0200 (CEST)","from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net\n\t[IPv6:2001:4b98:dc4:8::223])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id C879A603E7\n\tfor ;\n\tThu, 28 Jul 2022 08:47:12 +0200 (CEST)","(Authenticated sender: jacopo@jmondi.org)\n\tby mail.gandi.net (Postfix) with ESMTPSA id 9641360006;\n\tThu, 28 Jul 2022 06:47:10 +0000 (UTC)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=libcamera.org;\n\ts=mail; t=1658990834;\n\tbh=d0uPRpteM/+XxhxSfIy8I//MxcqVtJiMDKmo6fmlQmM=;\n\th=Date:To:References:In-Reply-To:Subject:List-Id:List-Unsubscribe:\n\tList-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:\n\tFrom;\n\tb=GENEzYmd4wNbVd0qrVrE9pVLbRneJvzxXX29pBgOB9AhlbJOc/8LFxIUgWq66mSYV\n\tk8oiYHpF74bsVAof3kqDpDT5b2qziurHS4hz7nwD6L2VJlN7zWRlZHsJMECBEgd758\n\txKMosrzNBiIEZbmM7iWcth0HnN5DiD4UyHzkurDcJslt65tDZwOlr8RWWdGUd3Pgd4\n\tyMNf8k2DRYtluro1f6UzxUZceWhQWACOKf/2NajKRjUF6PwtW5ZO/mD71NAg9q7lbf\n\txJrDG+tOPAb9WUt4jLr3znreUU1NOcF4+nip7NzAbbn6fYQP6orq1ZZ2mGlxQPpb20\n\tZaDO3NTeLtlGQ==","Date":"Thu, 28 Jul 2022 08:47:05 +0200","To":"Laurent Pinchart ","Message-ID":"<20220728064705.3pxw7ndxo3dgia7u@uno.localdomain>","References":"<20220727222149.30627-1-laurent.pinchart@ideasonboard.com>\n\t<20220727222149.30627-2-laurent.pinchart@ideasonboard.com>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<20220727222149.30627-2-laurent.pinchart@ideasonboard.com>","Subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","From":"Jacopo Mondi via libcamera-devel ","Reply-To":"Jacopo Mondi ","Cc":"libcamera-devel@lists.libcamera.org","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":24216,"web_url":"https://patchwork.libcamera.org/comment/24216/","msgid":"","date":"2022-07-28T10:30:48","subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","submitter":{"id":2,"url":"https://patchwork.libcamera.org/api/people/2/","name":"Laurent Pinchart","email":"laurent.pinchart@ideasonboard.com"},"content":"Hi Jacopo,\n\nOn Thu, Jul 28, 2022 at 08:47:05AM +0200, Jacopo Mondi wrote:\n> Hi Laurent\n> \n> On Thu, Jul 28, 2022 at 01:21:41AM +0300, Laurent Pinchart via libcamera-devel wrote:\n> > The std::optional::value_or(U &&default_value) function returns the\n> > contained value if available, or \\a default_value if the std::optional\n> \n> Are the \\a in the commit message intended ?\n\nOops :-) I'll drop it.\n\n> > has no value. If the desired default value is a default-constructed T,\n> > the obvious option is to call std::optional::value_or(T{}). This\n> > approach has two drawbacks:\n> >\n> > - The \\a default_value T{} is constructed even if the std::optional\n> > instance has a value, which impacts efficiency.\n> > - The T{} default constructor needs to be spelled out explicitly in the\n> > value_or() call, leading to long lines if the type is complex.\n> >\n> > Introduce a defopt variable that solves these issues by providing a\n> > value that can be passed to std::optional::value_or() and get\n> > implicitly converted to a default-constructed T.\n> >\n> > Signed-off-by: Laurent Pinchart \n> > ---\n> > include/libcamera/base/utils.h | 14 +++++++++\n> > src/libcamera/base/utils.cpp | 21 +++++++++++++\n> > test/utils.cpp | 54 ++++++++++++++++++++++++++++++++++\n> > 3 files changed, 89 insertions(+)\n> >\n> > diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h\n> > index cfff05836de7..889bb4a2270e 100644\n> > --- a/include/libcamera/base/utils.h\n> > +++ b/include/libcamera/base/utils.h\n> > @@ -361,6 +361,20 @@ decltype(auto) abs_diff(const T &a, const T &b)\n> > \t\treturn a - b;\n> > }\n> >\n> > +namespace details {\n> > +\n> > +struct defopt_t {\n> > +\ttemplate\n> > +\toperator T() const\n> > +\t{\n> > +\t\treturn T{};\n> > +\t}\n> > +};\n> > +\n> > +} /* namespace details */\n> > +\n> > +constexpr details::defopt_t defopt;\n> > +\n> \n> Clever! this indeed explains how it works:\n> \n> template< class U >\n> constexpr T value_or( U&& default_value ) const&;\n> \n> Equivalent to bool(*this) ? **this : static_cast(std::forward(default_value))\n> \n> \n> Reviewed-by: Jacopo Mondi \n> \n> > } /* namespace utils */\n> >\n> > #ifndef __DOXYGEN__\n> > diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp\n> > index 6a307940448e..9cd6cb197243 100644\n> > --- a/src/libcamera/base/utils.cpp\n> > +++ b/src/libcamera/base/utils.cpp\n> > @@ -463,6 +463,27 @@ std::string toAscii(const std::string &str)\n> > * \\a b\n> > */\n> >\n> > +/**\n> > + * \\var defopt\n> > + * \\brief Constant used with std::optional::value_or() to create a\n> > + * default-constructed object\n> > + *\n> > + * The std::optional::value_or(U &&default_value) function returns the\n> > + * contained value if available, or \\a default_value if the std::optional has no\n> > + * value. If the desired default value is a default-constructed T, the obvious\n> > + * option is to call std::optional::value_or(T{}). This approach has two\n> > + * drawbacks:\n> > + *\n> > + * * The \\a default_value T{} is constructed even if the std::optional instance\n> > + * has a value, which impacts efficiency.\n> > + * * The T{} default constructor needs to be spelled out explicitly in the\n> > + * value_or() call, leading to long lines if the type is complex.\n> > + *\n> > + * The defopt variable solves these issues by providing a value that can be\n> > + * passed to std::optional::value_or() and get implicitly converted to a\n> > + * default-constructed T.\n> > + */\n> > +\n> > } /* namespace utils */\n> >\n> > #ifndef __DOXYGEN__\n> > diff --git a/test/utils.cpp b/test/utils.cpp\n> > index d65467b5102c..129807a63ec6 100644\n> > --- a/test/utils.cpp\n> > +++ b/test/utils.cpp\n> > @@ -7,6 +7,7 @@\n> >\n> > #include \n> > #include \n> > +#include \n> > #include \n> > #include \n> > #include \n> > @@ -169,6 +170,55 @@ protected:\n> > \t\treturn TestPass;\n> > \t}\n> >\n> > +\tint testDefopt()\n> > +\t{\n> > +\t\tstatic bool defaultConstructed = false;\n> > +\n> > +\t\tstruct ValueType {\n> > +\t\t\tValueType()\n> > +\t\t\t\t: value_(-1)\n> > +\t\t\t{\n> > +\t\t\t\tdefaultConstructed = true;\n> > +\t\t\t}\n> > +\n> > +\t\t\tValueType(int value)\n> > +\t\t\t\t: value_(value)\n> > +\t\t\t{\n> > +\t\t\t}\n> > +\n> > +\t\t\tint value_;\n> > +\t\t};\n> > +\n> > +\t\t/*\n> > +\t\t * Test that utils::defopt doesn't cause default-construction\n> > +\t\t * of a ValueType instance when value_or(utils::defopt) is\n> > +\t\t * called on a std::optional that has a value.\n> > +\t\t */\n> > +\t\tstd::optional opt = ValueType(0);\n> > +\t\tValueType value = opt.value_or(utils::defopt);\n> > +\n> > +\t\tif (defaultConstructed || value.value_ != 0) {\n> > +\t\t\tstd::cerr << \"utils::defopt didn't prevent default construction\"\n> > +\t\t\t\t << std::endl;\n> > +\t\t\treturn TestFail;\n> > +\t\t}\n> > +\n> > +\t\t/*\n> > +\t\t * Then test that the ValueType is correctly default-constructed\n> > +\t\t * when the std::optional has no value.\n> > +\t\t */\n> > +\t\topt = std::nullopt;\n> > +\t\tvalue = opt.value_or(utils::defopt);\n> > +\n> > +\t\tif (!defaultConstructed || value.value_ != -1) {\n> > +\t\t\tstd::cerr << \"utils::defopt didn't cause default construction\"\n> > +\t\t\t\t << std::endl;\n> > +\t\t\treturn TestFail;\n> > +\t\t}\n> > +\n> > +\t\treturn TestPass;\n> > +\t}\n> > +\n> > \tint run()\n> > \t{\n> > \t\t/* utils::hex() test. */\n> > @@ -281,6 +331,10 @@ protected:\n> > \t\tif (testDuration() != TestPass)\n> > \t\t\treturn TestFail;\n> >\n> > +\t\t/* utils::defopt test. */\n> > +\t\tif (testDefopt() != TestPass)\n> > +\t\t\treturn TestFail;\n> > +\n> > \t\treturn TestPass;\n> > \t}\n> > };","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id E3219C3275\n\tfor ;\n\tThu, 28 Jul 2022 10:30:52 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id A099E63312;\n\tThu, 28 Jul 2022 12:30:52 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 7A3096330D\n\tfor ;\n\tThu, 28 Jul 2022 12:30:51 +0200 (CEST)","from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi\n\t[62.78.145.57])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id DBF5656D;\n\tThu, 28 Jul 2022 12:30:50 +0200 (CEST)"],"DKIM-Signature":["v=1; 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dkim=pass (1024-bit key; \n\tunprotected) header.d=ideasonboard.com\n\theader.i=@ideasonboard.com\n\theader.b=\"LoY9hVYs\"; dkim-atps=neutral","Date":"Thu, 28 Jul 2022 13:30:48 +0300","To":"Jacopo Mondi ","Message-ID":"","References":"<20220727222149.30627-1-laurent.pinchart@ideasonboard.com>\n\t<20220727222149.30627-2-laurent.pinchart@ideasonboard.com>\n\t<20220728064705.3pxw7ndxo3dgia7u@uno.localdomain>","MIME-Version":"1.0","Content-Type":"text/plain; charset=utf-8","Content-Disposition":"inline","In-Reply-To":"<20220728064705.3pxw7ndxo3dgia7u@uno.localdomain>","Subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","From":"Laurent Pinchart via libcamera-devel\n\t","Reply-To":"Laurent Pinchart ","Cc":"libcamera-devel@lists.libcamera.org","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}},{"id":24236,"web_url":"https://patchwork.libcamera.org/comment/24236/","msgid":"","date":"2022-07-29T07:10:21","subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","submitter":{"id":123,"url":"https://patchwork.libcamera.org/api/people/123/","name":"Florian Sylvestre","email":"fsylvestre@baylibre.com"},"content":"Hi Laurent,\n\nOn Thu, 28 Jul 2022 at 12:30, Laurent Pinchart via libcamera-devel\n wrote:\n>\n> Hi Jacopo,\n>\n> On Thu, Jul 28, 2022 at 08:47:05AM +0200, Jacopo Mondi wrote:\n> > Hi Laurent\n> >\n> > On Thu, Jul 28, 2022 at 01:21:41AM +0300, Laurent Pinchart via libcamera-devel wrote:\n> > > The std::optional::value_or(U &&default_value) function returns the\n> > > contained value if available, or \\a default_value if the std::optional\n> >\n> > Are the \\a in the commit message intended ?\n>\n> Oops :-) I'll drop it.\n>\n> > > has no value. If the desired default value is a default-constructed T,\n> > > the obvious option is to call std::optional::value_or(T{}). This\n> > > approach has two drawbacks:\n> > >\n> > > - The \\a default_value T{} is constructed even if the std::optional\n> > > instance has a value, which impacts efficiency.\n> > > - The T{} default constructor needs to be spelled out explicitly in the\n> > > value_or() call, leading to long lines if the type is complex.\n> > >\n> > > Introduce a defopt variable that solves these issues by providing a\n> > > value that can be passed to std::optional::value_or() and get\n> > > implicitly converted to a default-constructed T.\n> > >\n> > > Signed-off-by: Laurent Pinchart \n> > > ---\n> > > include/libcamera/base/utils.h | 14 +++++++++\n> > > src/libcamera/base/utils.cpp | 21 +++++++++++++\n> > > test/utils.cpp | 54 ++++++++++++++++++++++++++++++++++\n> > > 3 files changed, 89 insertions(+)\n> > >\n> > > diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h\n> > > index cfff05836de7..889bb4a2270e 100644\n> > > --- a/include/libcamera/base/utils.h\n> > > +++ b/include/libcamera/base/utils.h\n> > > @@ -361,6 +361,20 @@ decltype(auto) abs_diff(const T &a, const T &b)\n> > > return a - b;\n> > > }\n> > >\n> > > +namespace details {\n> > > +\n> > > +struct defopt_t {\n> > > + template\n> > > + operator T() const\n> > > + {\n> > > + return T{};\n> > > + }\n> > > +};\n> > > +\n> > > +} /* namespace details */\n> > > +\n> > > +constexpr details::defopt_t defopt;\n> > > +\n> >\n> > Clever! this indeed explains how it works:\n> >\n> > template< class U >\n> > constexpr T value_or( U&& default_value ) const&;\n> >\n> > Equivalent to bool(*this) ? **this : static_cast(std::forward(default_value))\n> >\n> >\n> > Reviewed-by: Jacopo Mondi \n> >\n> > > } /* namespace utils */\n> > >\n> > > #ifndef __DOXYGEN__\n> > > diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp\n> > > index 6a307940448e..9cd6cb197243 100644\n> > > --- a/src/libcamera/base/utils.cpp\n> > > +++ b/src/libcamera/base/utils.cpp\n> > > @@ -463,6 +463,27 @@ std::string toAscii(const std::string &str)\n> > > * \\a b\n> > > */\n> > >\n> > > +/**\n> > > + * \\var defopt\n> > > + * \\brief Constant used with std::optional::value_or() to create a\n> > > + * default-constructed object\n> > > + *\n> > > + * The std::optional::value_or(U &&default_value) function returns the\n> > > + * contained value if available, or \\a default_value if the std::optional has no\n> > > + * value. If the desired default value is a default-constructed T, the obvious\n> > > + * option is to call std::optional::value_or(T{}). This approach has two\n> > > + * drawbacks:\n> > > + *\n> > > + * * The \\a default_value T{} is constructed even if the std::optional instance\n> > > + * has a value, which impacts efficiency.\n> > > + * * The T{} default constructor needs to be spelled out explicitly in the\n> > > + * value_or() call, leading to long lines if the type is complex.\n> > > + *\n> > > + * The defopt variable solves these issues by providing a value that can be\n> > > + * passed to std::optional::value_or() and get implicitly converted to a\n> > > + * default-constructed T.\n> > > + */\n> > > +\n> > > } /* namespace utils */\n> > >\n> > > #ifndef __DOXYGEN__\n> > > diff --git a/test/utils.cpp b/test/utils.cpp\n> > > index d65467b5102c..129807a63ec6 100644\n> > > --- a/test/utils.cpp\n> > > +++ b/test/utils.cpp\n> > > @@ -7,6 +7,7 @@\n> > >\n> > > #include \n> > > #include \n> > > +#include \n> > > #include \n> > > #include \n> > > #include \n> > > @@ -169,6 +170,55 @@ protected:\n> > > return TestPass;\n> > > }\n> > >\n> > > + int testDefopt()\n> > > + {\n> > > + static bool defaultConstructed = false;\n> > > +\n> > > + struct ValueType {\n> > > + ValueType()\n> > > + : value_(-1)\n> > > + {\n> > > + defaultConstructed = true;\n> > > + }\n> > > +\n> > > + ValueType(int value)\n> > > + : value_(value)\n> > > + {\n> > > + }\n> > > +\n> > > + int value_;\n> > > + };\n> > > +\n> > > + /*\n> > > + * Test that utils::defopt doesn't cause default-construction\n> > > + * of a ValueType instance when value_or(utils::defopt) is\n> > > + * called on a std::optional that has a value.\n> > > + */\n> > > + std::optional opt = ValueType(0);\n> > > + ValueType value = opt.value_or(utils::defopt);\n> > > +\n> > > + if (defaultConstructed || value.value_ != 0) {\n> > > + std::cerr << \"utils::defopt didn't prevent default construction\"\n> > > + << std::endl;\n> > > + return TestFail;\n> > > + }\n> > > +\n> > > + /*\n> > > + * Then test that the ValueType is correctly default-constructed\n> > > + * when the std::optional has no value.\n> > > + */\n> > > + opt = std::nullopt;\n> > > + value = opt.value_or(utils::defopt);\n> > > +\n> > > + if (!defaultConstructed || value.value_ != -1) {\n> > > + std::cerr << \"utils::defopt didn't cause default construction\"\n> > > + << std::endl;\n> > > + return TestFail;\n> > > + }\n> > > +\n> > > + return TestPass;\n> > > + }\n> > > +\n> > > int run()\n> > > {\n> > > /* utils::hex() test. */\n> > > @@ -281,6 +331,10 @@ protected:\n> > > if (testDuration() != TestPass)\n> > > return TestFail;\n> > >\n> > > + /* utils::defopt test. */\n> > > + if (testDefopt() != TestPass)\n> > > + return TestFail;\n> > > +\n> > > return TestPass;\n> > > }\n> > > };\n>\n> --\n> Regards,\n>\n> Laurent Pinchart\n\nReviewed-by: Florian Sylvestre ","headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 4DAB7C3275\n\tfor ;\n\tFri, 29 Jul 2022 07:10:37 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id A932263312;\n\tFri, 29 Jul 2022 09:10:36 +0200 (CEST)","from mail-pl1-x635.google.com (mail-pl1-x635.google.com\n\t[IPv6:2607:f8b0:4864:20::635])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id A50F360486\n\tfor ;\n\tFri, 29 Jul 2022 09:10:34 +0200 (CEST)","by mail-pl1-x635.google.com with SMTP id o3so3839927ple.5\n\tfor ;\n\tFri, 29 Jul 2022 00:10:34 -0700 (PDT)"],"DKIM-Signature":["v=1; 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charset=\"UTF-8\"","Subject":"Re: [libcamera-devel] [PATCH v5 1/9] libcamera: base: utils:\n\tProvide defopt to simplify std::optional::value_or() usage","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","From":"Florian Sylvestre via libcamera-devel\n\t","Reply-To":"Florian Sylvestre ","Cc":"libcamera-devel@lists.libcamera.org","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "}}]