Question

I’m trying to save a nested lambda function in Visual Studio 2012.

class Wrap
{
public:
  typedef function<void(Wrap*)> Method;
  Method method;
  std::map<string, Wrap> methods;
};

Wrap x;
x.method = [](Wrap *arg) {
    Wrap::Method t = [](Wrap*) {};
    arg->methods["child"].method = t;
};

Which produces this error:

error C2678: binary '<' : no operator found which takes a left-hand operand of type const std::string (or there is no acceptable conversion)

I can’t make heads or tails of this error.

I have tested this in g++ and clang. They can compile it.
http://liveworkspace.org/code/4kVlUY$72

How would i make Visual Studio to compile it? Any workaround?

Answer 1

The problem is completely unrelated to what you expect:

#include <string>

solves it. Seems like the comparison operators require <string> to be included explicitly, while the class itself is defined if you include just <map>.