c++ - SFINAE overload choice for has or has not operator<<? -


consider these 2 functions:

template <class type,            class = typename std::enable_if</*has operator <<*/>::type> void f(std::ostream& stream, const type& value);  template <class type,            class... dummytypes,           class = typename std::enable_if<sizeof...(dummytypes) == 0>::type> void f(std::ostream& stream, const type& value, dummytypes...);

as non-variadic overload has priority on variadic overload, want check whether type has operator<< std::ostream using std::enable_if in first version.

so should write instead of /*has operator <<*/ ?

the following should work

template <class type,            class = decltype(std::declval<std::ostream&>() << std::declval<type>())> void f(std::ostream& stream, const type& value) {     stream << value; }

(note don't need use std::enable_if in case)


Comments

Post a Comment

Popular posts from this blog

java.util.scanner - How to read and add only numbers to array from a text file -

i'm learning java , have question regarding reading file want read numbers file contains strings well. here example of file: 66.56 "3 java 3-43 5-42 2.1 1 and here coding: public class test { public static void main (string [] args){ if (0 < args.length) { file x = new file(args[0]); try{ scanner in = new scanner( new fileinputstream(x)); arraylist<double> test = new arraylist<>(); while(in.hasnext()){ if(in.hasnextdouble()){ double f=in.nextdouble(); test.add(f);} else {in.next();} } catch(ioexception e) { system.err.println("exception during reading: " + e); } } my problem add 66.56,2.1 , 1 doesn't add 3 after "3 or ignores 3-43 , 5-42 can tell me how skip strings , add doubles here? thanks all said 3 ie; "3, 3-43 , 4-42 strings either u read string , split , check number @ " , - or put in space between characters , integers. jvm after compilation tre
Read more

rewrite - Trouble with Wordpress multiple custom querystrings -

i'm working on adding multiple querystring , doesn't seem work. i've found codes seems work others might i'm missing something. i want like: http://mydomain.com/board/?getyear=2013&getsometext2=sometext to http://mydomain.com/board/2013/sometext/ i added code below functions.php file. doesn't seem work should though. this works. echoing querystring gets both variable without problem. http://mydomain.com/board/2013/sometext/ but doesn't. tested querystring vis isset() seems nothing being set/get http://mydomain.com/board/2013/ function add_query_vars($vars) { $vars[] = "getyear"; $vars[] = "getsometext2"; return $vars; } add_filter('query_vars', 'add_query_vars'); function add_rewrite_rules($arules) { $anewrules = array('board/([^/]+)/([^/]+)/?$' => 'index.php?pagename=board&getyear=$matches[1]&getsometext2=$matches[2]'); $arules = $a
Read more

php - Accessing static methods using newly created $obj or using class Name -

see class definition below: i using 5.3.9 version of php class a{ static function ab(){ echo "static function ab<br>"; } public function xy(){ echo "public function xy<br>"; } } $obj = new a(); $obj->ab(); a::ab(); both functions call give same output without error static function ab static function ab how possible static method can called class object? because static method calls using class name only?! now difference between accessing these 2 ways call static method ? referring php.net website declaring class properties or methods static makes them accessible without needing instantiation of class. property declared static can not accessed instantiated class object (though static method can). a big difference is because static methods callable without instance of object created, pseudo-variable $this not available inside method declared static. refer page php.net/manual/en/
Read more