Re: Template argument determination

From	Ruben Safir <ruben@mrbrklyn.com>
Newsgroups	comp.lang.c++
Subject	Re: Template argument determination
Date	Tue, 24 May 2011 18:08:32 +0000 (UTC)
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On Tue, 24 May 2011 12:32:59 -0500, A. Bolmarcich wrote:

>> I'm having trouble understanding why my program is making a change in
>> the argument type of my template class function
> 
> A short answer is that what you are seeing is due to an implicit
> conversion that is part of the C++ programming language.  If you do not
> want this implicit conversion done, declare the constructor being used
> by the implicit conversion as explcit, as it
> 
>   class Distribution {
>   public:
>     explicit Distribution(int i) {
>       // whatever the constructor does
>     }
>   }
> 
> What follows are details, with most of the source you gave snipped down
> to essentials.
> 
>>    template < class T >
>>       void List<T>::find_value(T val)
>>       {
> [snip]
>>       }
> 
> [snip]
> 
>> 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){
> [snip]
>> 	 chainlist::List<stats::Distribution<T> > * dump;
> 
>> 		 dump->find_value(search_val);
> [snip]
>>       }
> 
> [snip]
> 
> The expression
> 
>   stats::mean_list(tallies, 7 )
> 
> implicitly instantiates the mean_list function template.  Due to the
> argument types, the instantiated function includes the declaration
> 
>   chainlist::List<stats::Distribution<int> > * dump;
> 
> The expression
> 
>   dump->find_value(search_val)
> 
> implicitly instantiates the find_value member function template. Due to
> the type of the object for which the member function is called, the
> instantiated member function is
> 
>   void List<stats::Distribution<int> >::find_value(
>         stats::Distribution<int> val)
> 
> In the call to that function by dump->find_value(search_val), an
> implicit conversion by constructor is done to convert the search_val
> argument (of type int) to a stats::Distribution<int> (the type of the
> parameter).



Bingo - thanks for taking the time to give me this explanation.  But its not
capable of doing this implicit conversation unless T is defined as an int.
The compiler couldn't deduce this otherwise.


Ruben

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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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