Re: Template argument determination

Newsgroups	comp.lang.c++
From	"A. Bolmarcich" <aggedor@earl-grey.cloud9.net>
Subject	Re: Template argument determination
References	<irh227$8du$1@dont-email.me> <slrnitob96.77f.aggedor@earl-grey.cloud9.net> <irhdh7$na0$1@dont-email.me> <slrnitqfiq.10rf.aggedor@earl-grey.cloud9.net> <irlu67$6kt$2@reader1.panix.com>
Message-ID	<slrnitt6od.23jf.aggedor@earl-grey.cloud9.net> (permalink)
Date	2011-05-26 13:25 -0500

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On 2011-05-26, Ruben Safir <ruben@mrbrklyn.com> wrote:
> On Wed, 25 May 2011 12:37:30 -0500, A. Bolmarcich wrote:

[snip]
>> I snipped from your post all but what you wrote and explained the
>> difference between using
>> 
>>   foo(42)
>> 
>> and
>> 
>>   foo<int>(42)
>> 
>> in the example you wrote.  With foo(42), the function template argument
>> was neither explicitly specified nor deduced, and the template was not
>> instantiated.
>>
>
>
> I don't understand this.

I'll break it into smaller pieces.  The expression

  foo(42)

does not explicity specify a template argument; the expression

  foo<int>(42)

explicitly specifies a template argument.

With the expression foo(42) the compiler is not able to deduce the
template argument (T) for

  template <class T>
  void foo(X<T>) {}

because the rules for template argument deduction do not include one
that matches the int function argument (42) with the function
parameter type X<T>.

[snip]

>> What Ruben wrote was: "But its not capable of doing this implicit
>> conversion unless T is defined as an int."  Your reading missed some of
>> the words Ruben wrote.  I wrote that an implicit conversion from
>> function arguments to function parameters should be done even if T is
>> defined as something other than an int.  
>
> See the language started to get very confusing.  We have template 
> parameters, function parameters, template arguments, function 
> arguments...my head is swiming and to make it harder, you keep 
> substituting structs for classes.

In the function declaration

  void f1(int fp)

fp is a function parameter.  In the function call

  f1(42)

42 is a function argument.  In the template

  template <class T>
  void f2(T x) {}

T is a template parameter.  In the function call

  f2<int>(42)

int is a template argument.  It is an explicitly specified template
argument.

In C++ a struct is a class whose members are public by default.
Using a struct instead of a class in short examples eliminates the
need to add

  public:

in a class to make the example compile.

[snip]

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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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