c++ - How to use `is_member_function_pointer` to include/exclude member function calls in algorithms? -

I am attempting to use within an algorithm, either to make a specific call to a specific member function Do not do anything (if it exists) or do anything:

  template & lt; Class T & gt; Struct is_member_function_pointer;   
 
 Checks whether T is a non-static member function pointer. Member provides stable value which is equal to true, if T is a non-static member function pointer type. Otherwise, the value is equal to wrong.   
 For example:  
  #include & lt; Iostream & gt; # Include & lt; Type_traits & gt; #include & lt; Vector & gt; Struct a {zero bow () console {std :: cout & lt; & Lt; "Boo." & Lt; & Lt; Std :: endl; }}; Structure B {}; The template's & lt; Bool & gt; Loose structure; The template's & lt; & Gt; Strip bioyabel & lt; True> {Template & lt; Typename type & gt; Static zero booIt (type const & amp; t) {t .boo (); }}; The template's & lt; & Gt; Strip bioyabel & lt; False & gt; {Template & lt; Typename type & gt; Static zero byte (typecast & amp; t) {std :: cout & lt; & Lt; "Non-bioyable type of burden" & lt; & Lt; Std :: endl; }}; Template & lt; Typename type & gt; Zero alg (type const & amp; t) {booable & lt; Std :: is_member_function_pointer & lt; Decltype (& type :: boo) & gt; :: value & gt; :: booIt (t); } Int main (int argc, const char * argv []) {a a; BB; Alg (a); Alg (b); Return 0; }   
 The structure is  a  is  booable  and  b  is not. The algorithm is dependent on the  alg ,  is_member_function_pointer  inside the boolean value to  false  or  true  if it depends on the fact that The  type  implements a member function  bu . This Boolean value is then used to specialize in the  booable  structure, which implements the  booIt  stable member function whose sole purpose call  boo  Booable object, or  do nothing and notify the user   
 However, it is compiled (saved IM  main.cpp ) , Result in the following compile time error:  
  main.cpp: in a type of futuristic alge (const type & amp;) [instant = b] With: main.cpp: 46: 10: here is the main.cpp: 37: 54: error: a ?? ?? Booâ ???? Not a member of "BA" booable & LT; Std :: is_member_function_pointer & lt; Decltype (& type :: buoy) & gt; :: Price & gt; :: booIt (t);   
 I wonder: is not  a usable boolean value and a compile-time error  to indicate this attribute? This is the same error that is just done by me  
  B; B.boo ();   
 What have I done here?  
  
 
 
 
 This is not reporting as usable boolean values ​​and this property structure issue Not a compile time error?   
 Yes, but to test a member of a member, that member needs survival.  
 You get an error because  b  does not have  boo  and result in  alg   decltype (and b :: BOO) . You will not expect to compile  decltype (& int :: foo) , do you want  
 what you want     
   
 For example  
 
          
 A specialist template that gives you further examination to use the results of the investigation.  
 Edit:  
 An easy way to check for  boo  by using the expression SFINAE:  
  template & Lt; Typename T & gt; Constexpr Auto is_booable (int) - & gt; Fall (std :: declval & lt; T & gt; () .boo (), boole ()) {back true; } Template & lt; Typename T & gt; Constexpr bool is_booable (...) {return false; }   
 Usage:  
  booable & lt; Is_booable & lt; Type & gt; (0) & gt; :: booIt (t);   
 More.