Bind Vs Lambda?

Question

I have a question about which style is preferred: std::bind Vs lambda in C++0x. I know that they serve -somehow- different purposes but lets take an example of intersecting functionality.

Using lambda:

uniform_int<> distribution(1, 6);
mt19937 engine;
// lambda style
auto dice = [&]() { return distribution(engine); };

Using bind:

uniform_int<> distribution(1, 6);
mt19937 engine;
// bind style
auto dice = bind(distribution, engine);

Which one should we prefer? why? assuming more complex situations compared to the mentioned example. i.e. What are the advantages/disadvantages of one over the other?

Answer 1

C++0x lambdas are monomorphic, while bind can be polymorphic. You cannot have something like

auto f = [](auto a, auto b) { cout << a << ' ' << b; }
f("test", 1.2f);

a and b must have known types. On the other hand, tr1/boost/phoenix/lambda bind allows you to do this:

struct foo
{
  typedef void result_type;

  template < typename A, typename B >
  void operator()(A a, B b)
  {
    cout << a << ' ' << b;
  }
};

auto f = bind(foo(), _1, _2);
f("test", 1.2f); // will print "test 1.2"

Note that the types A and B are not fixed here. Only when f is actually used these two will be deduced.