typedef 默认模板类型为同名

Question

Original question: I have a type template <typename CostType> struct Key which I use in another class UQueue , which is also templated on CostType . I'd like to not have to specify Key<CostType> within this class. I tried typedef Key<CostType> Key , which did not work. Is there another workaround?

Edit: The minimal example that would have exhibited the problem (if there had been one), would have been this:

template <typename T>
class C1 {
    T t;
};
template <typename T>
class C2 {
    typedef C1<T> C1;
    C1 c1;
};

However, this works ( using MSVC 2010 ). I have some other error in my code which confused me into believing the typedef was illegal. Sorry about the bandwidth.

Answer 1

Use a macro. That's how I always do it since it's simple and easy to maintain.

Take this situation:

template <typename A, size_t B, int C, pointer_to_some_func D> class tTemplate
{
     struct myStruct
     {
         int i, j;
     };

     void function1 (tTemplate <A, B, C, D> :: myStruct S);
     void function2 ();
};

template <typename A, size_t B, int C, pointer_to_some_func D> void tTemplate <A, B, C, D> :: function1 (tTemplate <A, B, C, D> :: myStruct S)
{  
}

etc...

Imagine if I had to change an argument or add another one...

Now, with this:

#define dTemplate tTemplate <A, B, C, D>
#define sTemplate template <typename A, size_t B, int C, pointer_to_some_func D>

sTemplate void dTemplate :: function1 (dTemplate::myStruct S)
{

}

Easier to maintain, useable by other classes\templates etc. One template argument change = a macro change which applies everywhere. And it is also nicer to the eyes. Also, I find it a good thing in templates, especially since typedefs are no-go. And best thing about macros, even IF typedefs were a standard: you don't need forward declarations for them... ever, (yeah, macros are evil, but in situations like theese, they're more than useful)

As for your example:

#define dC1 C1 <T>       // no ";" !!!

template <typename T> class C1
{
    T t;
};

template <typename T> class C2
{
    dC1 c1;
};