Remove reference in decltype (return T instead of T& where T& is the decltype)

To remove a reference:

#include <type_traits>

static_assert(std::is_same<int, std::remove_reference<int&>::type>::value, "wat");

In your case:

template <typename T>
auto doSomething(const T& foo)
    -> typename std::remove_reference<decltype(foo.bar())>::type
{
    return foo.bar();
}

Just to be clear, note that as written returning a reference is just fine:

#include <type_traits>

struct f
{
    int& bar() const
    {
        static int i = 0;
        return i;
    } 
};

template <typename T>
auto doSomething(const T& foo)
    -> decltype(foo.bar())
{ 
    return foo.bar();
}

int main()
{
    f x;
    return doSomething(x);
}

The returned reference can simply be passed on without error. Your example in the comment is where it becomes important and useful:

template <typename T>
auto doSomething(const T& foo)
    -> decltype(foo.bar())
{ 
    return foo.bar() + 1; // oops
}