typedefs in class templates and their (non)inheritance

[=?big5?b?YWxleGh1YW5nKLbAsVLAcyk=?= <alexhuang at gorilla dot com dot tw>]

Are typedefs in class templates required to be redeclared in descendents?

The following code does not compile using gcc 4.2.2
-----------------------------------
template <typename T>
struct MyFunctor : public std::unary_function<int, T>
{
    result_type operator()(argument_type arg)
    {
        return arg;
    }
};

MyFunctor<int> foo;
-----------------------------------
error: ISO C++ forbids declaration of ¡¥result_type¡¦ with no type

The compiler says that result_type and argument_type are not defined.  They are defined in std::unary_function, but apparently not inherited.  There is a thread http://gcc.gnu.org/ml/gcc-bugs/1997-10/msg00045.html which explains that these typedefs cannot be inherited because std::unary_function may be specialized on <int, int> and the typedefs might not exist in that specialization.  Can't the compiler discover whether or not the specialization exists and hence whether or not the typedefs exist?  Redeclaring typedefs seems a bit error-prone to me -- plus, I'm lazy.

The following code does compile using gcc 4.2.2
-----------------------------------
template <typename T>
struct MyFunctor : public std::unary_function<int, T>
{
    typedef typename std::unary_function<int, T>::result_type result_type;
    typedef typename std::unary_function<int, T>::argument_type argument_type;

    result_type operator()(argument_type arg)
    {
        return arg;
    }
};

MyFunctor<int> foo;
-----------------------------------

Am I missing some other construct that will make std::unary_function's typedefs visible in MyFunctor?

Thanks,
Alex