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Re: Template argument determination

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On Mon, 23 May 2011 20:31:25 +0000, Ruben Safir wrote:

> I'm having trouble understanding why my program is making a change in
> the argument type of my template class function
> 
>    template < class T >
>       void List<T>::find_value(T val)
>       {
> 	 cursor() = front();
> 	 while(cursor() != endd()){
> 	    if (*(cursor()->value()) == val)
> 	       return;
> 	    else{
> 	       cursor(cursor()->next());
> 	    }
> 	 }
> 	 if(*(endd()->value()) == val)
> 	    return;
> 	 else{
> 	    cursor() = 0; //park the cursor when nothing is found
> 	 }
>       }
> 
> 
> It's part of a List template class
> 
> I call it from a templated fucntion in a different namespace as follows:
> 
> 
> tally = new chainlist::List<stats::Distribution<int> >; tallies = new
> chainlist::List< chainlist::List< stats::Distribution<int> > *>;
> 
> std::cout << "The standard mean for picking 7 is ==> " <<
> stats::mean_list(tallies, 7 ) << std::endl;;
> 
>    template<typename T>
>       float mean_list(chainlist::List<
>       chainlist::List<stats::Distribution<T> >*  > *  tallies, T
>       search_val){
> 	 if(tallies->endd() == 0){
> 	    std::cout << "Empty List" << std::endl; return 0.0;
> 	 }
> 	 int sum = 0;
> 	 chainlist::List<stats::Distribution<T> > * dump; tallies->cursor
() =
> 	 tallies->front(); while(tallies->cursor() != tallies->endd() ){
> 		 //tallies->cursor()->value()->find_value(search_val); 
dump =
> 		 *(tallies->cursor()->value()); //dump->cursor() = dump-
>endd();
> 		 //std::cout << "Testing\n" << *(dump->cursor()->value()) 
<<
> 		 std::endl; dump->find_value(search_val);
> 		 if(dump->cursor() != NULL)
> 		    sum +=  dump->cursor()->value()->population();
> 		 tallies->cursor(tallies->cursor()->next());
> 	 }
> 	 dump = *(tallies->cursor()->value()); dump->find_value
(search_val);
> 	 if(dump->cursor() != 0)
> 	    sum +=  dump->cursor()->value()->population();
> 	 float tot = (float) sum/(float)(tallies->size()); std::cout << 
"Mean "
> 	 << tot << " sum " << sum << " size " << tallies->size() << 
std::endl;
> 	 return tot;
> 
>       }
> 
> Now T is an integer for mean_list, and the first argument is of type
> 
> chainlist::List< chainlist::List<stats::Distribution<int> >*  > * when
> called and the second argument is of type int
> 
> I then pass int search_val to method chainlist::List<T>::find_value(T)
> where T = stats::Distribution<T> (where T is an int) on this line:
> 
> dump->find_value(search_val);
> 
> and that's where the weirdness happens.  I have a type mismatch since
> I'm sending by value an integer instead of a stats::Distribution<T>
> 
> Instead the program calls the stat::Distribution constructor using 7,
> the value of search_val, as an argument redrawing search_val as type to
> a Distribution<int>
> 
> :in gdb
> 
> 
>  312       void List<T>::find_value(T val) 313       {
>  314          cursor() = front();
>  315          while(cursor() != endd()){ 316             if
>  (*(cursor()->value()) == val) 317                return;
>  318             else{
>  319                cursor(cursor()->next()); 320             }
>  321          }
>  322          if(*(endd()->value()) == val) 323             return;
>  324          else{
>  325             cursor() = 0; //park the cursor when nothing is found
>  326          }
>  327       }
> 
> chainlist::List<stats::Distribution<int> >::find_value (this=0x804f008,
> val=...) at linklist.h:314 (gdb) ptype val
> type = class stats::Distribution<int> {
>   public:
>     chainlist::List<stats::Distribution<int> > *tally;
>   private:
>     int freq;
>     int occurances;
> 
>   public:
>     void Distribution(int, int);
>     void Distribution(void);
>     int description(void) const;
>     int population(void) const;
>     void increase_occ(void);
>     void descrease_occ(void);
>     int operator()(void);
>     bool operator==(stats::Distribution<int> &); bool
>     operator<(stats::Distribution<int> &); float
>     stddev(chainlist::List<stats::Distribution<int> > *);
> }
> 
> 
> What rule for Template argument matching allows for this kind of magic?

i knew nobody would have an insight on this :(

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Thread

Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-23 20:31 +0000
  Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-24 02:50 +0000
    Re: Template argument determination Michael Doubez <michael.doubez@free.fr> - 2011-05-24 03:48 -0700
    Re: Template argument determination "Balog Pal" <pasa@lib.hu> - 2011-05-24 13:06 +0200
      Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-24 14:44 +0000
        Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-24 15:04 +0000
          Re: Template argument determination "Balog Pal" <pasa@lib.hu> - 2011-05-24 17:33 +0200
          Re: Template argument determination Victor Bazarov <v.bazarov@comcast.invalid> - 2011-05-24 11:43 -0400
  Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-24 12:32 -0500
    Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-24 18:08 +0000
      Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-24 14:32 -0500
        Re: Template argument determination Victor Bazarov <v.bazarov@comcast.invalid> - 2011-05-24 15:48 -0400
          Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-24 17:11 -0500
            Re: Template argument determination Victor Bazarov <v.bazarov@comcast.invalid> - 2011-05-24 19:04 -0400
              Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-25 12:37 -0500
                Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-26 16:12 +0000
                Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-26 13:25 -0500
            Re: Template argument determination Ruben Safir <ruben@mrbrklyn.com> - 2011-05-25 02:47 +0000
              Re: Template argument determination "Balog Pal" <pasa@lib.hu> - 2011-05-25 10:06 +0200
              Re: Template argument determination "A. Bolmarcich" <aggedor@earl-grey.cloud9.net> - 2011-05-25 12:40 -0500

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