Example of using lambda as a comparator for unordered_set

t-unordered_set_comp.cc

#include <iostream>
#include <string>
#include <unordered_set>
#include <functional>
#include <assert.h>

using namespace std;
struct Foo {
  string name;
};

int main() {
  Foo* f1 = new Foo();
  f1->name = "foo1";
  Foo* f2 = new Foo();
  f2->name = "foo2";

  auto comp = [](const Foo* a, const Foo* b) {
    return a->name == b->name;
  };

  unordered_set<Foo*, std::hash<Foo*>, decltype(comp)> st(10, std::hash<Foo*>(), comp);
  assert(st.insert(f1).second);
  assert(! st.insert(f1).second);
}