I'm wondering why I a compile error in the following:
#include <unordered_map>
template <typename T_Key, typename T_Value>
class Iterator
{public:
//std::unordered_map<T_Key, T_Value>::iterator iter; // GIVES ERROR syntax error: identifier 'iterator'
std::unordered_map<int, int>::iterator iter; // WORKS
};
Should be
typename std::unordered_map<T_Key, T_Value>::iterator iter;
iterator is what's known as a dependent name, because it's meaning cannot be known without knowing what T_Key and T_Value are. Therefore the compiler needs a hint as to what kind of entity it is. Syntactically it could be a type name or it could be a static class member. typename tells the compiler that it's a type.
I believe C++ rules have changed or are changing on this subject, and typename is required less frequently than before. In contexts where the name can only reasonably be a type, typename will no longer be necessary. Maybe someone else can provide the full details.
