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Andrew · Guest

Hello all:

Is there a standard means of using the for_each algorithm on an STL
container of smart pointers? Here is the solution I have so far, but
it might be obsolete:

// compose.h
#ifndef COMPOSE_MY_H
#define COMPOSE_MY_H
# include <functional>
/* class for composition f(g(x)) */
template<class OP1, class OP2>
class compose_f_gx_t
: public std::unary_function<typename OP2::argument_type,
typename OP1::result_type>
{
private:
OP1 op1; // process: op1(op2(x))
OP2 op2;
public:
compose_f_gx_t(const OP1& o1, const OP2& o2) : op1(o1), op2(o2) { }
typename OP1::result_type operator()(const typename
OP2::argument_type& x) const
{ return op1(op2(x)); }
};

template<class OP1, class OP2>
inline compose_f_gx_t<OP1,OP2>
compose_f_gx(const OP1& o1, const OP2& o2)
{ return compose_f_gx_t<OP1,OP2>(o1,o2); }
#endif COMPOSE_MY_H

// memfun1b.cpp
#include <iostream>
#include <string>
#include <vector>
#include <algorithm> // for for_each
#include <functional> // for mem_fun_ref and mem_fun
#include <boost/shared_ptr.hpp> // for boost::shared_ptr<>
#include "compose.h" // for compose_f_gx

using namespace std;

class Person
{
private:
string first;
string last;
public:
Person(const string& f, const string& l) : first(f), last(l) { }
virtual ~Person() { }
virtual void print() const
{ cout << first << " " << last << endl; }
/* ... */
};

int main()
{
typedef boost::shared_ptr vector<Ptr> coll;
coll.push_back(Ptr(new Person("Joe","Powers")));
coll.push_back(Ptr(new Person("Tariq","Aslam")));
coll.push_back(Ptr(new Person("Andrew","Henrick")));
coll.push_back(Ptr(new Person("Suzanne","Henrick")));
coll.push_back(Ptr(new Person("Bill","Henrick")));

cout << "Ask each element to print itself: " << endl;
for_each(coll.begin(),coll.end(),

compose_f_gx(mem_fun_ref(&Person::print),mem_fun_ref(&Ptr::operator*)));
cout << endl;

cout << "Ask each element to print itself: " << endl;
for_each(coll.begin(),coll.end(),

compose_f_gx(mem_fun(&Person::print),mem_fun_ref(&Ptr::get)));
cout << endl;
}

This compiles and runs on gcc 3.3 (Apple) and with boost 1.33.1. Two
solutions are given.

Thanks for your input.
Andrew

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Peter Dimov · Guest

Andrew wrote:

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