Heterogeneous polymorphic vector sorting example in C++11

20130507.cpp

#include <string>
#include <iostream>
#include <tuple>
#include <memory>
#include <algorithm>
using namespace std;

typedef tuple<string, int, string> sort_key_t;

class AnimalBase {
    virtual ostream & out(ostream &) = 0;
  public:
    virtual sort_key_t get_key() = 0;
    friend ostream & operator<<(ostream & os, AnimalBase &a) { return a.out(os); }
};

class Cow : public AnimalBase {
    string name_;
    int age_;
    virtual sort_key_t get_key() override { return sort_key_t("cow", age_, name_); }
    virtual ostream & out(ostream & os) override {
        return os << "A cow age " << age_ << " named " << name_ << endl;
    }
  public:
    Cow(string name, int age) : name_(name), age_(age) {}
};

class Dog : public AnimalBase {
    string name_;
    int age_;
    virtual sort_key_t get_key() override { return sort_key_t("dog", age_, name_); }
    virtual ostream & out(ostream & os) override {
        return os << "A dog age " << age_ << " named " << name_ << endl;
    }
  public:
    Dog(string name, int age) : name_(name), age_(age) {}
};

class Kitty : public AnimalBase {
    string name_;
    int age_;
    virtual sort_key_t get_key() override { return sort_key_t("kitty", age_, name_); }
    virtual ostream & out(ostream & os) override {
        return os << "A kitty age " << age_ << " named " << name_ << endl;
    }
  public:
    Kitty(string name, int age) : name_(name), age_(age) {}
};

int main()
{
    vector<unique_ptr<AnimalBase>> barnyard;
    barnyard.emplace_back(new Kitty("Puss-n-boots", 2));
    barnyard.emplace_back(new Kitty("Mr. Pickles", 2));
    barnyard.emplace_back(new Dog("Fifo", 3));
    barnyard.emplace_back(new Cow("Bluebell", 6));
    barnyard.emplace_back(new Dog("Muttsworth", 2));
    barnyard.emplace_back(new Cow("Bessy", 6));
   
    cout << "Before sort:\n";
    for(auto & a : barnyard)
        cout << *a;
    
    sort(begin(barnyard), end(barnyard), [](const unique_ptr<AnimalBase> & a, const unique_ptr<AnimalBase> & b) {
        return a->get_key() < b->get_key(); });
    
    cout << "\n\nAfter sorting by species then age then name:\n";
    for(auto & a : barnyard)
        cout << *a;
}
    

output.txt

$ g++ -Wall -Wextra -pedantic -std=c++11 -O2 20130507.cpp -o 20130507 && ./20130507
Before sort:
A kitty age 2 named Puss-n-boots
A kitty age 2 named Mr. Pickles
A dog age 3 named Fifo
A cow age 6 named Bluebell
A dog age 2 named Muttsworth
A cow age 6 named Bessy


After sorting by species then age then name:
A cow age 6 named Bessy
A cow age 6 named Bluebell
A dog age 2 named Muttsworth
A dog age 3 named Fifo
A kitty age 2 named Mr. Pickles
A kitty age 2 named Puss-n-boots