Re: for_each loop on a map without a functor

From:
"Daniel T." <daniel_t@earthlink.net>
Newsgroups:
microsoft.public.vc.stl,comp.lang.c++
Date:
Sun, 20 Jan 2008 18:47:00 -0500
Message-ID:
<daniel_t-EFCB71.18470020012008@earthlink.vsrv-sjc.supernews.net>
In article
<c77e194e-cdfa-44b3-bf4b-d023bd5940b8@y5g2000hsf.googlegroups.com>,
 nguillot <nicolas.guillot@gmail.com> wrote:

On 18 jan, 22:13, "Daniel T." <danie...@earthlink.net> wrote:

On Jan 18, 3:41 pm, nguillot <nicolas.guil...@gmail.com> wrote:

On 18 jan, 21:03, "Daniel T." <danie...@earthlink.net> wrote:

On Jan 18, 5:45 am, nguillot <nicolas.guil...@gmail.com> wrote:

So the question: how write the for_each line?


Hmm, the for_each line I wrote above compiles fine for me. What
compiler are you using?


I tried on VC++ 6.0 and on visual studio 2005...
and you


Visual Sutdio 2005 compiles the following just fine:
=== begine code ===
#include <algorithm>
#include <map>

using namespace std;

typedef int k;

class d {
public:
   void setIntMember( int i ) { }

};

template < typename Pair, typename Op >
class CallFuncOn2nd_t {
   Op fn;
public:
   CallFuncOn2nd_t( Op fn ): fn(fn) { }
   typename Op::result_type operator()( Pair& v ) const {
      return fn( v.second );
   }

};

template < typename Pair, typename Op >
CallFuncOn2nd_t<Pair, Op> callFuncOn2nd( Op fn ) {
   return CallFuncOn2nd_t<Pair, Op>( fn );

}

typedef std::map<k, d> tMap;

int main(){
   tMap m;
   for_each(m.begin(), m.end(),

callFuncOn2nd<tMap::value_type>( bind2nd( mem_fun_ref( &d::setIntMember ),
4 ) ) );}

=== end code ===


ARF !!

It's my fault.
I had not seen the function callOn2nd. I only saw the class!
So, ok, the code compiles (on g++).

I don't understand why we can't define only the class (if we do that
and call directly the class in the for_each:
for_each(m.begin(),
m.end(),CallFuncOn2nd_t<tMap::value_type>(bind2nd(mem_fun_ref(&d::setIntMember
),
4)));
it doesn't compile:
wrong number of template arguments (1, should be 2) provided for
`template<class Pair, class Op> class CallFuncO
n2nd_t')

the same loop with the function is ok.
I would think that in
     CallFuncOn2nd_t<tMap::value_type>(bind2nd(...)
the constructor would "set" the Op template arg, the second being
specified between <>.


The compiler will not infer types on template classes, only functions.
Both template parameters must be declared when using the class directly.
i.e., you would have to do this:

   for_each( m.begin(), m.end(),
      CallFuncOn2nd_t< tMap::value_type,
      binder2nd< mem_fun1_ref_t< void, d, int> > >(
      bind2nd( mem_fun_ref( &d::setIntMember ), 4 ) ) );

So this solution is ok, modify the object within the map, not a
temporary.


I think the boost bind solution is better.

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