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  1. #include <type_traits>
  2. #include <iostream>
  3.  
  4. namespace named {
  5.     struct param {};
  6.  
  7.     template<class wantparam, class wanttype, class curparamname, class curparamtype, class...Rest, 
  8.         class allowed=typename std::enable_if<!std::is_same<wantparam,typename std::decay<curparamname>::type>::value>::type
  9.     >
  10.     wanttype get(curparamname, curparamtype&&, Rest&&...rest) 
  11.     {
  12.         static_assert(std::is_base_of<param,typename std::decay<curparamname>::type>::value,"value passed to named parameter list without a name");
  13.         static_assert(!std::is_base_of<param,typename std::decay<curparamtype>::type>::value,"name passed to named parameter list without a value");
  14.         return get<wantparam,wanttype>(rest...);
  15.     }
  16.  
  17.     template<class wantparam, class wanttype, class curparamtype, class...Rest>
  18.     wanttype get(wantparam, curparamtype&& value, Rest&&...) 
  19.     {
  20.         static_assert(std::is_base_of<param,typename std::decay<wantparam>::type>::value,"value passed to named parameter list without a name");
  21.         static_assert(!std::is_base_of<param,typename std::decay<curparamtype>::type>::value,"name passed to named parameter list without a value");
  22.         return std::forward<curparamtype>(value);
  23.     }
  24.  
  25.     template<class wantparam, class wanttype, class curparamtype>
  26.     wanttype get(curparamtype) 
  27.     {
  28.         static_assert(std::is_base_of<param,typename std::decay<curparamtype>::type>::value,"value passed to named parameter list without a name");
  29.         static_assert(!std::is_base_of<param,typename std::decay<curparamtype>::type>::value,"name passed to named parameter list without a value");
  30.     }
  31.  
  32.     template<class wantparam, class wanttype>
  33.     wanttype get() 
  34.     {static_assert(sizeof(wantparam)==0,"missing required named parameter");}
  35.  
  36.  
  37.     //add parameter names here.  Make sure they all have unique types and inherit from param.
  38.     static struct a_type : public param{} a;
  39.     static struct b_type : public param{} b;
  40.     static struct c_type : public param{} c;
  41. }
  42.  
  43. void my_func(int a, int b = 0, int c = 0){
  44.     std::cout << a << ' ' << b << ' ' << c << '\n';
  45. }
  46.  
  47. template<class curparamname, class...Rest, 
  48.     class allowed=typename std::enable_if<std::is_base_of<named::param,typename std::decay<curparamname>::type>::value>::type
  49. >
  50. void my_func(curparamname p, Rest...rest) {
  51.     return my_func(
  52.         named::get<named::a_type,int>(p, rest...),
  53.         named::get<named::b_type,int>(p, rest..., named::b, 0),
  54.         named::get<named::c_type,int>(p, rest..., named::c, 0)
  55.         );
  56. }
  57.  
  58. int main() {
  59.     my_func(3);
  60.     my_func(3, 4);
  61.     my_func(3, 4, 5);
  62.     my_func(named::c, 6, named::a, 7);
  63.     //my_func(named::b, 8); //error C2338: missing required named parameter
  64.     my_func(named::c, 9, named::b, 10, named::a, 11);
  65.     //my_func(named::c, 12, 13, named::a, 14); //error C2338: value passed to named parameter list without a name
  66.     //my_func(named::c, named::a, 15); //error C2338: named passed to named parameter list without a value
  67.     return 0;
  68. }
Success #stdin #stdout 0s 3344KB
comments (?)
stdin
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Standard input is empty
stdout
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3 0 0
3 4 0
3 4 5
7 0 6
11 10 9
https://ideone.com/U6tHa2
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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