Sorting SimpleCashFlows in QuantLib

Question

I would like to sort SimpleCashFlow(s) according to date. I am having trouble incorporing the the less than function < in std::sort

#include <iostream>
#include <algorithm> 
#include <ql/time/date.hpp>
#include <ql/time/period.hpp>
#include <ql/cashflows/simplecashflow.hpp>

using namespace QuantLib;
int main()
{
  Date date(1, January, 2021);
  Date date2(1, January, 2020);
  Real amount = 100.0;

 
  ext::shared_ptr<SimpleCashFlow> cf1(new SimpleCashFlow(amount,date));
  ext::shared_ptr<SimpleCashFlow> cf2(new SimpleCashFlow(amount,date2));
  Leg leg;
  leg.push_back(cf1);
  leg.push_back(cf2);

  std::sort(leg.begin(),leg.end());
 
  for (auto& c : leg){ 
    std::cout << c->date() << " , " << c->amount()  << std::endl;
  }
  
  return 0;
} 

Answer 1

Using a lambda, you can write something like

std::sort(leg.begin(), leg.end(),
          [](const ext::shared_ptr<CashFlow>& c1,
             const ext::shared_ptr<CashFlow>& c2){ return c1->date() < c2->date() });

If you can use C++14, the above can be simplified to

std::sort(leg.begin(), leg.end(),
          [](auto c1, auto c2){ return c1->date() < c2->date() });

This works for all cashflow types, not just SimpleCashFlow.