definition of template parameter 'a' shadows template parameter 'a'

Question

#include <vector>

template < class a > class innervec {
    inner();
    ~inner();

    std::vector<a> innerdata;
};

template < class a, template <class a> class inner > class outer {
    outer();
    ~outer();

    a *myPtr;
    inner<a> myInner;
};

//Edit to provide examples

template < class a > class innerlist {
     otherinner();
     ~otherinner();
    
    std::list<a> innerdata
}

//call sites

//Use outer with vector inner with int type
outer<int, innervec> OuterWithVec()

//Use outer with list inner with double type
outer<double, innerlist> OuterWithList()

https://godbolt.org/z/j3ofqE4fj

Similar question Can a parameter of a template template parameter cause shadowing?

I'm attempting to refactor some code, and with a newer compiler I get this error. I understand that is not valid C++, but The original question doesn't seem to directly answer "What is the correct solution?"

In this case I simply want to pass the same template parameter to the inner template parameter, right now my outer template class only has a pointer of the template type, and a member of type "inner templated class" where the inner parameter is simply passed through. (I think this was the original purpose of this design).

The thing is that "pass the template parameter to the inner template parameter" is not a logical statement. The "inner template" is an independent template that takes one template parameter. There's nothing to "pass". The only time `a` might come into play would be when ***instantiating*** the inner template. That's something that ***doesn't*** happen in a template declaration. So, it's unclear what this is supposed to do. Simply remove the inner template parameter's name. The End. — Sam Varshavchik, Jul 07 '21 at 00:03
I'm not sure what the issue is. Why are you naming the type of the template template parameter at all? What are you trying to do with that? — cigien, Jul 07 '21 at 00:04
Look at your error message. The compiler points to the two things named `a` that are problematic. To which of these two things do you want to refer in the two lines where you *use* `a`? (The two lines are the definitions of `myPtr` and `myInner`.) Once you know that, ask yourself why the other thing needs to have the same name, or even a name at all. — JaMiT, Jul 07 '21 at 00:45
@SamVarshavchik So I guess I meant to say, the original intent looks like "I defined a class that has a templated type as a member, as well as containing a member of the templated parameter type directly." "I need to ensure that the type of the inner and the type of the member agree" — Joshua, Jul 07 '21 at 12:54
@cigien so what name are you talking about, and why don't I need it? — Joshua, Jul 07 '21 at 12:55
Your class currently takes 2 template parameters, and there's no relationship between them (until you use the first as a parameter for the second inside the class). Can you please add an example of how you want to use this class? What does it look like at the call site? — cigien, Jul 07 '21 at 12:59

definition of template parameter 'a' shadows template parameter 'a'

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