Re: Template argument determination

Newsgroups	comp.lang.c++
From	"A. Bolmarcich" <aggedor@earl-grey.cloud9.net>
Subject	Re: Template argument determination
References	<ireg6t$5nh$1@reader1.panix.com>
Message-ID	<slrnitnqub.1fk.aggedor@earl-grey.cloud9.net> (permalink)
Date	2011-05-24 12:32 -0500

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> 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).

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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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