c++ - Passing STL algorithm to another function -

i have vector of user defined type (student). have 2 functions identical except single function call inside them.

here 2 functions:

student lowest_grade(const std::vector<student> &all_students){   return *std::min_element(std::begin(all_students), std::end(all_students),       [](const student &a, const student &b){     return a.get_average() < b.get_average();}); }  student highest_grade(const std::vector<student> &all_students){   return *std::max_element(std::begin(all_students), std::end(all_students),       [](const student &a, const student &b){     return a.get_average() < b.get_average();}); } 

both of these functions working correctly use seems constructed better. want create function pass in either min_element or max_element, like:

template <typename func> student dispatch(const std::vector<student> &all_students, func){   return *func(std::begin(all_students), std::end(all_students),       [](const student &a, const student &b){     return a.get_average() < b.get_average();}); } 

but can't manage work properly. not sure how go doing this.

edit - how calling dispatch function + error message:

std::cout<<"lowest: "<< dispatch(all_students, std::max_element); 

the error message is:

g++ m.cpp -std=c++11 -wall -o main m.cpp: in function ‘int main()’: m.cpp:86:63: error: missing template arguments before ‘(’ token    std::cout<<"lowest: "<< dispatch(all_students, std::function(std::max_element));                                                                ^ ryan@ryan-virtualbox:~/desktop/prog/daily/167m$ make g++ m.cpp -std=c++11 -wall -o main m.cpp: in function ‘int main()’: m.cpp:86:81: error: no matching function call ‘dispatch(std::vector<student>&, <unresolved overloaded function type>)’    std::cout<<"lowest: "<< dispatch<std::function>(all_students, std::max_element);                                                                                  ^ m.cpp:86:81: note: candidate is: m.cpp:71:9: note: template<class func> student dispatch(const std::vector<student>&, func)  student dispatch(const std::vector<student> &all_students, func){          ^ m.cpp:71:9: note:   template argument deduction/substitution failed: 

your function can written way want follows:

template<typename func> student dispatch(const std::vector<student> &all_students, func func) {     assert(!all_students.empty());     return *func(std::begin(all_students), std::end(all_students),                   [](const student &a, const student &b){                    return a.get_average() < b.get_average();}); } 

and invoked as

dispatch(students,           std::min_element<decltype(students)::const_iterator,                            bool(*)(const student&, const student&)>); dispatch(students,           std::max_element<decltype(students)::const_iterator,                            bool(*)(const student&, const student&)>); 

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you can cut down on verbosity quite bit if implement operator< student. allow omit template argument comparator.

template<typename func> student dispatch(const std::vector<student> &all_students, func func) {     assert(!all_students.empty());     return *func(std::begin(all_students), std::end(all_students)); }  dispatch(students,           std::min_element<decltype(students)::const_iterator>); dispatch(students,           std::max_element<decltype(students)::const_iterator>); 

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yet way this, call min_element within dispatch, pass in comparators different behaviors.

template<typename comparator> student dispatch(const std::vector<student> &all_students, comparator comp) {     assert(!all_students.empty());     return *std::min_element(std::begin(all_students), std::end(all_students),                               comp); }  dispatch(students, std::less<student>()); dispatch(students, std::greater<student>());  // requires operator> student 

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finally, if you're going fetch both lowest , highest grades, standard library offers std::minmax_element fetch both in single call.

auto minmax = std::minmax_element(std::begin(students), std::end(students)); 

live demo of different options.