[libcamera-devel] [PATCH] libcamera: utils: Add map_keys() function

[Umang Jain]

Hi Laurent,

I have a query below.

On 6/25/20 6:53 AM, Laurent Pinchart wrote:
> Add a map_keys() function to the utils namespace to extract keys from a
> map.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>   include/libcamera/internal/utils.h | 10 ++++++++++
>   src/libcamera/utils.cpp            |  7 +++++++
>   test/utils.cpp                     | 21 +++++++++++++++++++++
>   3 files changed, 38 insertions(+)
>
> diff --git a/include/libcamera/internal/utils.h b/include/libcamera/internal/utils.h
> index 0953423ee8d0..4fe4843922a9 100644
> --- a/include/libcamera/internal/utils.h
> +++ b/include/libcamera/internal/utils.h
> @@ -11,6 +11,7 @@
>   #include <chrono>
>   #include <memory>
>   #include <ostream>
> +#include <set>
>   #include <sstream>
>   #include <string>
>   #include <string.h>
> @@ -36,6 +37,15 @@ const char *basename(const char *path);
>   char *secure_getenv(const char *name);
>   std::string dirname(const std::string &path);
>   
> +template<typename T>
> +std::set<typename T::key_type> map_keys(const T &map)
> +{
> +	std::set<typename T::key_type> keys;
> +	std::transform(map.begin(), map.end(), std::inserter(keys, keys.end()),
I am not able to wrap my head around keys.end() as the beginning 
position for the
insertor? keys.end() points to `past-the-end`element which should not be 
de-referenced,
as claimed in the online docs. Can you explain why we cannot use:

std::inserter(keys, keys.begin()) ?

> +		       [](const auto &value) { return value.first; });
> +	return keys;
> +}
> +
>   template<class InputIt1, class InputIt2>
>   unsigned int set_overlap(InputIt1 first1, InputIt1 last1,
>   			 InputIt2 first2, InputIt2 last2)
> diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
> index d55338fe681a..1eb8970a5bbc 100644
> --- a/src/libcamera/utils.cpp
> +++ b/src/libcamera/utils.cpp
> @@ -127,6 +127,13 @@ std::string dirname(const std::string &path)
>   	return path.substr(0, pos + 1);
>   }
>   
> +/**
> + * \fn std::set<typename T::key_type> map_keys(const T &map)
> + * \brief Retrieve the keys of a std::map<>
> + * \param[in] map The map whose keys to retrieve
> + * \return A std::set<> containing the keys of \a map
> + */
> +
>   /**
>    * \fn libcamera::utils::set_overlap(InputIt1 first1, InputIt1 last1,
>    *				     InputIt2 first2, InputIt2 last2)
> diff --git a/test/utils.cpp b/test/utils.cpp
> index 66b91f1203e1..a9d072030f1c 100644
> --- a/test/utils.cpp
> +++ b/test/utils.cpp
> @@ -6,6 +6,8 @@
>    */
>   
>   #include <iostream>
> +#include <map>
> +#include <set>
>   #include <sstream>
>   #include <string>
>   #include <vector>
> @@ -144,6 +146,25 @@ protected:
>   		if (TestPass != testDirname())
>   			return TestFail;
>   
> +
> +		/* utils::map_keys() test. */
> +		const std::map<std::string, unsigned int> map{
> +			{ "zero", 0 },
> +			{ "one", 1 },
> +			{ "two", 2 },
> +		};
> +		const std::set<std::string> expectedKeys{
> +			"zero",
> +			"one",
> +			"two",
> +		};
> +
> +		const std::set<std::string> keys = utils::map_keys(map);
> +		if (keys != expectedKeys) {
> +			cerr << "utils::map_keys() test failed" << endl;
> +			return TestFail;
> +		}
> +
>   		return TestPass;
>   	}
>   };