c++ - "Overload" function template based on function object operator() signature -

-

consider example of function template takes function reference first argument. overloaded based on function signature of first argument. body of each overload feeds 1st argument function appropriately it's signature.

template<typename t> struct mapttot { typedef t (type)(const t); };  template<typename t> std::vector<t> map_vec(         const typename mapttot<t>::type& fnc,         const std::vector<t>& source) {     std::vector<t> dest;     dest.reserve(source.size());     (const auto : source)     {         dest.emplace_back(fnc(i));     }     return dest; }  template<typename t> struct maptandvectot { typedef t (type)(const t, const std::vector<t>&); };  template<typename t> std::vector<t> map_vec(         const typename maptandvectot<t>::type& fnc,         const std::vector<t>& source) {     std::vector<t> dest;     dest.reserve(source.size());     (const auto : source)     {         dest.emplace_back(fnc(i, source));     }     return dest; }

because of overload, reference either of these functions can passed 1st arg:

int foo(const int x); int bar(const int x, const std::vector<int>& v);

and doing transparent:

const auto = map_vec(foo, v); const auto b = map_vec(bar, v);

the overloading strategy used above won't work function objects since object doesn't have signature per se. suppose function objects of interest following.

class addnum { public:     addnum(const int num) : num_(num) {}      int operator()(const int x) const     {         return x + num_;     }  private:     const int num_; };  class addnummulsize { public:     addnummulsize(const int num) : num_(num) {}      int operator()(const int x, const std::vector<int>& v) const     {         return (x + num_) * v.size();     }  private:     const int num_; };

how can change function templates accept both function objects , functions , overload based on how call should made?

specifically, want compile:

const addnum add2(2); const auto c = map_vec(add2, v);  const addnummulsize add2mulsz(2); const auto d = map_vec(add2mulsz, v);

the error message clang gives quite clear , matches expect.

error: no matching function call 'map_vec'

candidate function [with t = int] not viable: no known conversion 'const addnum' 'typename mapttot::type &' (aka 'int (&)(const int)') 1st argument

update: c++98 version of question

“overload” function template based on function object operator() signature in c++98

change signature generically take function object of type f, can use expression-sfinae restrict overloads based on f can called with:

template<typename f, typename t> auto map_vec(f&& fnc, const std::vector<t>& source)     -> decltype(void(fnc(std::declval<t>())), std::vector<t>{});  template<typename f, typename t> auto map_vec(f&& fnc, const std::vector<t>& source)     -> decltype(void(fnc(std::declval<t>(), source)), std::vector<t>{});

demo


Comments

Post a Comment

Popular posts from this blog

python - mat is not a numerical tuple : openCV error -

-
i have write down code showing error ma not getting it: please help: showing mat not numerical tuple: import cv import cv2 capture = cv2.videocapture("j.3gp") while(1): _, frame1 = capture.read() grayimage1 = cv2.cvtcolor(frame1, cv2.color_bgr2gray) _, frame2 = capture.read() grayimage2 = cv2.cvtcolor(frame2, cv2.color_bgr2gray) differenceimage = cv2.absdiff(grayimage1,grayimage2) thresholdimage = cv2.threshold(differenceimage,25,255,cv2.thresh_binary) cv2.imshow("difference image", differenceimage) cv2.imshow("threshold image", thresholdimage) cv2.imshow("image", frame1) k = cv2.waitkey(30) & 0xff error arising : ----------------------------------------------------------------------------------------- traceback (most recent call last): file "desk.py", line 15, in <module> cv2.imshow("threshold image", thresholdimage) typeerror: mat not numerical tuple ...
Read more

c# - MSAA finds controls UI Automation doesn't -

-
i'm working on automating windows application. i'm using teststack white framework. i've hit problem. program has 'window' object cannot see inside of. white shows no controls inside of it. inspect.exe shows no controls inside of either when running in ui automation mode. if switch inspect msaa see controls inside fine. there anyway me use msaa c# handle on these controls? if can identify msaa functions need, can use p/invoke call them c#. here's example article doing msaa: http://www.codeproject.com/articles/38906/ui-automation-using-microsoft-active-accessibility also, pinvoke.net can used identify iaccessible (msaa) functions: http://www.pinvoke.net/search.aspx?search=iaccessible&namespace=[all] here's answer along lines: msaa com-based? finally, alternative p/invoke, might able use tlbimp.exe create wrapper assembly oleacc.dll, , access msaa functions through it. i'm not sure if works msaa, it's worth try. as e...
Read more

wordpress - .htaccess: RewriteRule: bad flag delimiters -

-
pulling hair out on one. have following .htaccess file custom redirects in addition wordpress's default settings. when tested on local wamp server worked fine after moving production i'm not getting rewriterule: bad flag delimiters error in server log , after while site goes down internal server error any appreciated. in advance! <ifmodule mod_rewrite.c> rewriteengine on rewritebase / rewriterule ^rockford_weddings___welcome\.html$ /wedding/ [r=301,l] rewriterule ^blog/?$ /journal/ [r=301,l] rewriterule ^blog/(.*)$ /$1 [r=301,l] rewriterule ^portraitinvestment/?$ /portraitinvestment\.pdf [r=301,l] rewriterule ^weddinginvestment/?$ /weddinginvestment\.pdf [r=301,l] rewriterule ^holidaycards2014/?$ /holidaycards2014\.pdf [r=301,l] </ifmodule> # begin wordpress <ifmodule mod_rewrite.c> rewriteengine on rewritebase / rewriterule ^index\.php$ - [l] rewritecond %{request_filename} !-f rewritecond %{request_filename} !-d rewriterule . /index.php [l] </...
Read more