Functors versus lambdas

example_functors.cpp

#include "task.hpp"
#include <iostream>
#include <queue>
#include <vector>
#include <string>

using std::priority_queue;
using std::ostream;
using std::cout;
using std::string;
using std::less;
using std::vector;

int main()
{
   Task task1(1, "Laundry");
   Task task2(3, "Hackery");
   Task task3(2, "Grocery");
   priority_queue<Task, vector<Task>, less<Task>> q;
   q.push(task1);
   q.push(task2);
   q.push(task3);
   while (!q.empty()) {
       cout << q.top() << '\n';
       q.pop();
   }
}

example_lambdas.cpp

#include <iostream>
#include <queue>
#include <vector>
#include <string>

using std::priority_queue;
using std::ostream;
using std::cout;
using std::string;
using std::less;
using std::vector;

struct Task {
    int priority_;
    string description_;
    Task(int p, string d) : priority_(p), description_(d) {}
};

ostream& operator<<(ostream& os, const Task& t)
{
    os << t.priority_ << ": " << t.description_;
    return os;
}

int main()
{
   Task task1(1, "Laundry");
   Task task2(3, "Hackery");
   Task task3(2, "Grocery");
   auto compare_tasks = [](const Task& t1, const Task& t2) { return t1.priority_ < t2.priority_; };
   priority_queue<Task, vector<Task>, decltype(compare_tasks)> q(compare_tasks);
   q.push(task1);
   q.push(task2);
   q.push(task3);
   while (!q.empty()) {
       cout << q.top() << '\n';
       q.pop();
   }
}

Makefile

# Yeah, I am bad at writing Makefiles on the fly :(
all: example_functors.cpp example_lambdas.cpp  
	g++ -std=c++0x -g -Wall -Werror example_functors.cpp -o ef
	g++ -std=c++0x -g -Wall -Werror example_lambdas.cpp  -o el

task.hpp

#ifndef TASK_HPP
#define TASK_HPP

#include <iostream>
#include <string>

using std::ostream;
using std::string;

// example with prio_queues, then example with sort of vector
struct Task {
    int priority_;
    string description_;
    Task(int p, string d) : priority_(p), description_(d) {}
};

namespace std {
template<>
struct less<Task> {
    bool operator()(const Task& t1, const Task& t2)
    {
        return t1.priority_ < t2.priority_;
    }
};
}

ostream& operator<<(ostream& os, const Task& t)
{
    os << t.priority_ << ": " << t.description_;
    return os;
}


#endif // TASK_HPP