C++11 std::set lambda comparison function

It’s unlikely that the compiler will be able to inline a std::function call, whereas any compiler that supports lambdas would almost certainly inline the functor version, including if that functor is a lambda not hidden by a std::function.

You could use decltype to get the lambda’s comparator type:

#include <set>
#include <iostream>
#include <iterator>
#include <algorithm>

int main()
{
   auto comp = [](int x, int y){ return x < y; };
   auto set  = std::set<int,decltype(comp)>( comp );

   set.insert(1);
   set.insert(10);
   set.insert(1); // Dupe!
   set.insert(2);

   std::copy( set.begin(), set.end(), std::ostream_iterator<int>(std::cout, "\n") );
}

Which prints:

1
2
10

See it run live on Coliru.