Question

While defining the following lambda function

// file prog.hpp
template<typename T>
auto function = [](T& v){ return (v+= 2); }

I get the error:
error:template declaration of auto function

Please tell the correction that I should do

I am using g++-4.6.1 -std=c++0x -c prog.hpp

Answer 1

You can’t have templated lamdba expressions or closures. You can either make a templated traditional function, or a lambda factory (but the latter is more expensive):

template <typename T> T & TheFunction(T & v) { return v += 2; }

Or:

template <typename T> std::function<T&(T&)> MakeLambda() 
{
    return [](T & v) { return v+= 2; }
}