[boost] Re: yet another utility class(es)

From: jsiek_at_[hidden]
Date: 2000-02-16 00:43:33

Right, so in plain C++ speak, you need typename when using
the scope operator "::", and the type on the left-hand-side
of the :: is somehow dependent on a template type argument.

Need typenames for the first two examples, but not the second two.

template <class T>
void foo1(T x) {
  typedef typename T::yow Y;
} 

template <class T>
void foo2(T x) {
  typedef typename bar<T>::yow Y;
} 

template <class T>
void foo3(T x) {
  typedef T Y;
} 

void foo4(int x) {
  typedef bar<int>::yow Y;
} 

Aleksey Gurtovoy writes:
 > 
 > > 5. I think you may need "typename" on the "const T value_" and "T&
 > > variable_", and maybe the typedefs too.  I've never been able to figure
 > out
 > > what the requirements are.  Does anyone know of a good (easily
 > > understandable) reference for learning where typename is required?
 > >
 > 
 > I don't think so. From the section 14.6 [temp.res] of the standard ( para 5,
 > p. 258):
 > 
 > ... 'The keyword typename shall only be applied to qualified names, but
 > those names need not be dependent.'..
 > 
 > 'T&' and 'const T' are certainly not a 'qualified names' :)