how to correctly find out the return type of a lambda

Question

basically how to make following code compile?

I know it failed because compiler was trying to evaluate something like ([](int &i){})(0) but how to s

Answer 1

You may use following traits:

template 
struct return_type : return_type
{};
// For generic types, directly use the result of the signature of its 'operator()'

template 
struct return_type
{
    using type = ReturnType;
};