Detecting if an element is found inside a container












4












$begingroup$


I just wrote this template to detect if a given element is found inside a container:



template <typename Iterator> bool is_contained(Iterator begin, Iterator end, decltype(*begin) object)

{

    for (; begin != end; ++begin)

    {

        if (*begin == object)

        {

            return true;

        }

    }

    return false;

}


Which then would be called for examples as:



bool test = is_contained<decltype(container.begin())>(container.begin(), container.end(), anything);


This works fine, but I believe it is not so readable. I am also new to using decltype which makes me wonder if this would crash, and somehow I wont be calling the template correctly. Any feedback is highly appreciated.






c++ beginner template







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    4












    $begingroup$


    I just wrote this template to detect if a given element is found inside a container:



    template <typename Iterator> bool is_contained(Iterator begin, Iterator end, decltype(*begin) object)
    
{
    
    for (; begin != end; ++begin)
    
    {
    
        if (*begin == object)
    
        {
    
            return true;
    
        }
    
    }
    
    return false;
    
}


    Which then would be called for examples as:



    bool test = is_contained<decltype(container.begin())>(container.begin(), container.end(), anything);


    This works fine, but I believe it is not so readable. I am also new to using decltype which makes me wonder if this would crash, and somehow I wont be calling the template correctly. Any feedback is highly appreciated.






    c++ beginner template







    share|improve this question







    New contributor




    Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$















      4












      4








      4





      $begingroup$


      I just wrote this template to detect if a given element is found inside a container:



      template <typename Iterator> bool is_contained(Iterator begin, Iterator end, decltype(*begin) object)
      
{
      
    for (; begin != end; ++begin)
      
    {
      
        if (*begin == object)
      
        {
      
            return true;
      
        }
      
    }
      
    return false;
      
}


      Which then would be called for examples as:



      bool test = is_contained<decltype(container.begin())>(container.begin(), container.end(), anything);


      This works fine, but I believe it is not so readable. I am also new to using decltype which makes me wonder if this would crash, and somehow I wont be calling the template correctly. Any feedback is highly appreciated.






      c++ beginner template







      share|improve this question







      New contributor




      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      I just wrote this template to detect if a given element is found inside a container:



      template <typename Iterator> bool is_contained(Iterator begin, Iterator end, decltype(*begin) object)
      
{
      
    for (; begin != end; ++begin)
      
    {
      
        if (*begin == object)
      
        {
      
            return true;
      
        }
      
    }
      
    return false;
      
}


      Which then would be called for examples as:



      bool test = is_contained<decltype(container.begin())>(container.begin(), container.end(), anything);


      This works fine, but I believe it is not so readable. I am also new to using decltype which makes me wonder if this would crash, and somehow I wont be calling the template correctly. Any feedback is highly appreciated.






      c++ beginner template




      c++ beginner template






      share|improve this question







      New contributor




      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question







      New contributor




      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question






      New contributor




      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked Mar 27 at 19:04









      Daniel DuqueDaniel Duque

      555




      555




      New contributor




      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.





      New contributor





      Daniel Duque is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






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      Check out our Code of Conduct.






















          2 Answers
          2






          active

          oldest

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          8












          $begingroup$

          Note that for functions the compiler will detect the template types based on the parameters.

          So you can simply write:



          bool test = is_contained(container.begin(), container.end(), anything);


          I don't particularly like the use of decltype in your function. I would simply make it another template parameter.



          template <typename Iterator, typename Value>
          
bool is_contained(Iterator begin, Iterator end, Value const& object);


          Because of the compiler deducing the names you can use any type. Also this is more flexable as it allows you to use any type that is comparable to the type inside the container (rather than only allowing values that are the same type (or trivial convertible)).






          share|improve this answer









          $endgroup$





















            5












            $begingroup$



            1. Do you want to test whether an element is in a container, or an iterator-range?




              • The first allows for optimisation (taking advantage of the container's peculiarities). See "contains() algorithm for std::vector" for an example.

              • The second is more general in the absence of any range-library, like the one expected for the C++20 standard, and available for earlier versions.




            2. Constraining the needle to the type decltype(*begin) is very problematic:




              • It forces pass-by-value, which while it should be possible, at least with moveing, might be inefficient.

              • You cannot take advantage of transparent comparators (a C++14 feature), forcing the creation of a useless temporary. On the flip-side, if transparent comparators are not used, only a single temporary is constructed.

              • If the type is a proxy like with the dreaded std::vector <bool>, hilarity ensues.



            3. Consider taking advantage of the standard library, specifically std::find ().


            4. C++ will deduce the function's template-arguments perfectly fine, no need for error-prone verbosity.







            share|improve this answer









            $endgroup$













            • $begingroup$
              On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
              $endgroup$
              – Toby Speight
              Mar 28 at 22:09












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            2 Answers
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            active

            oldest

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            2 Answers
            2






            active

            oldest

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            active

            oldest

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            active

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            8












            $begingroup$

            Note that for functions the compiler will detect the template types based on the parameters.

            So you can simply write:



            bool test = is_contained(container.begin(), container.end(), anything);


            I don't particularly like the use of decltype in your function. I would simply make it another template parameter.



            template <typename Iterator, typename Value>
            
bool is_contained(Iterator begin, Iterator end, Value const& object);


            Because of the compiler deducing the names you can use any type. Also this is more flexable as it allows you to use any type that is comparable to the type inside the container (rather than only allowing values that are the same type (or trivial convertible)).






            share|improve this answer









            $endgroup$


















              8












              $begingroup$

              Note that for functions the compiler will detect the template types based on the parameters.

              So you can simply write:



              bool test = is_contained(container.begin(), container.end(), anything);


              I don't particularly like the use of decltype in your function. I would simply make it another template parameter.



              template <typename Iterator, typename Value>
              
bool is_contained(Iterator begin, Iterator end, Value const& object);


              Because of the compiler deducing the names you can use any type. Also this is more flexable as it allows you to use any type that is comparable to the type inside the container (rather than only allowing values that are the same type (or trivial convertible)).






              share|improve this answer









              $endgroup$
















                8












                8








                8





                $begingroup$

                Note that for functions the compiler will detect the template types based on the parameters.

                So you can simply write:



                bool test = is_contained(container.begin(), container.end(), anything);


                I don't particularly like the use of decltype in your function. I would simply make it another template parameter.



                template <typename Iterator, typename Value>
                
bool is_contained(Iterator begin, Iterator end, Value const& object);


                Because of the compiler deducing the names you can use any type. Also this is more flexable as it allows you to use any type that is comparable to the type inside the container (rather than only allowing values that are the same type (or trivial convertible)).






                share|improve this answer









                $endgroup$



                Note that for functions the compiler will detect the template types based on the parameters.

                So you can simply write:



                bool test = is_contained(container.begin(), container.end(), anything);


                I don't particularly like the use of decltype in your function. I would simply make it another template parameter.



                template <typename Iterator, typename Value>
                
bool is_contained(Iterator begin, Iterator end, Value const& object);


                Because of the compiler deducing the names you can use any type. Also this is more flexable as it allows you to use any type that is comparable to the type inside the container (rather than only allowing values that are the same type (or trivial convertible)).







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Mar 27 at 19:15









                Martin YorkMartin York

                74.2k488272




                74.2k488272

























                    5












                    $begingroup$



                    1. Do you want to test whether an element is in a container, or an iterator-range?




                      • The first allows for optimisation (taking advantage of the container's peculiarities). See "contains() algorithm for std::vector" for an example.

                      • The second is more general in the absence of any range-library, like the one expected for the C++20 standard, and available for earlier versions.




                    2. Constraining the needle to the type decltype(*begin) is very problematic:




                      • It forces pass-by-value, which while it should be possible, at least with moveing, might be inefficient.

                      • You cannot take advantage of transparent comparators (a C++14 feature), forcing the creation of a useless temporary. On the flip-side, if transparent comparators are not used, only a single temporary is constructed.

                      • If the type is a proxy like with the dreaded std::vector <bool>, hilarity ensues.



                    3. Consider taking advantage of the standard library, specifically std::find ().


                    4. C++ will deduce the function's template-arguments perfectly fine, no need for error-prone verbosity.







                    share|improve this answer









                    $endgroup$













                    • $begingroup$
                      On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                      $endgroup$
                      – Toby Speight
                      Mar 28 at 22:09
















                    5












                    $begingroup$



                    1. Do you want to test whether an element is in a container, or an iterator-range?




                      • The first allows for optimisation (taking advantage of the container's peculiarities). See "contains() algorithm for std::vector" for an example.

                      • The second is more general in the absence of any range-library, like the one expected for the C++20 standard, and available for earlier versions.




                    2. Constraining the needle to the type decltype(*begin) is very problematic:




                      • It forces pass-by-value, which while it should be possible, at least with moveing, might be inefficient.

                      • You cannot take advantage of transparent comparators (a C++14 feature), forcing the creation of a useless temporary. On the flip-side, if transparent comparators are not used, only a single temporary is constructed.

                      • If the type is a proxy like with the dreaded std::vector <bool>, hilarity ensues.



                    3. Consider taking advantage of the standard library, specifically std::find ().


                    4. C++ will deduce the function's template-arguments perfectly fine, no need for error-prone verbosity.







                    share|improve this answer









                    $endgroup$













                    • $begingroup$
                      On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                      $endgroup$
                      – Toby Speight
                      Mar 28 at 22:09














                    5












                    5








                    5





                    $begingroup$



                    1. Do you want to test whether an element is in a container, or an iterator-range?




                      • The first allows for optimisation (taking advantage of the container's peculiarities). See "contains() algorithm for std::vector" for an example.

                      • The second is more general in the absence of any range-library, like the one expected for the C++20 standard, and available for earlier versions.




                    2. Constraining the needle to the type decltype(*begin) is very problematic:




                      • It forces pass-by-value, which while it should be possible, at least with moveing, might be inefficient.

                      • You cannot take advantage of transparent comparators (a C++14 feature), forcing the creation of a useless temporary. On the flip-side, if transparent comparators are not used, only a single temporary is constructed.

                      • If the type is a proxy like with the dreaded std::vector <bool>, hilarity ensues.



                    3. Consider taking advantage of the standard library, specifically std::find ().


                    4. C++ will deduce the function's template-arguments perfectly fine, no need for error-prone verbosity.







                    share|improve this answer









                    $endgroup$





                    1. Do you want to test whether an element is in a container, or an iterator-range?




                      • The first allows for optimisation (taking advantage of the container's peculiarities). See "contains() algorithm for std::vector" for an example.

                      • The second is more general in the absence of any range-library, like the one expected for the C++20 standard, and available for earlier versions.




                    2. Constraining the needle to the type decltype(*begin) is very problematic:




                      • It forces pass-by-value, which while it should be possible, at least with moveing, might be inefficient.

                      • You cannot take advantage of transparent comparators (a C++14 feature), forcing the creation of a useless temporary. On the flip-side, if transparent comparators are not used, only a single temporary is constructed.

                      • If the type is a proxy like with the dreaded std::vector <bool>, hilarity ensues.



                    3. Consider taking advantage of the standard library, specifically std::find ().


                    4. C++ will deduce the function's template-arguments perfectly fine, no need for error-prone verbosity.








                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered Mar 27 at 20:04









                    DeduplicatorDeduplicator

                    11.8k1950




                    11.8k1950












                    • $begingroup$
                      On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                      $endgroup$
                      – Toby Speight
                      Mar 28 at 22:09


















                    • $begingroup$
                      On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                      $endgroup$
                      – Toby Speight
                      Mar 28 at 22:09
















                    $begingroup$
                    On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                    $endgroup$
                    – Toby Speight
                    Mar 28 at 22:09




                    $begingroup$
                    On point 2, it's even worse: you can't pass a value that's convertible to decltype(*begin), because templates need exact matches.
                    $endgroup$
                    – Toby Speight
                    Mar 28 at 22:09










                    Daniel Duque is a new contributor. Be nice, and check out our Code of Conduct.










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