[ 2010-12-07 Daniel comments and refines the proposed resolution ]

There is one further defect in the usage of result_of within reference_wrapper's function call operator: According to [refwrap.invoke] p. 1 the invokable entity of type T is provided as lvalue, but result_of is fed as if it were an rvalue. This does not only lead to potentially incorrect result types, but it will also have the effect that we could never use the function call operator with a function type, because the type encoding used in result_of would form an invalid function type return a function type. The following program demonstrates this problem:

#include <functional>

void foo(int) {}

int main()
{
   std::ref(foo)(0);  // error
}

The correct solution is to ensure that T becomes T& within result_of, which solves both problems at once.