Re: for_each loop on a map without a functor
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.