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Can I fill a template parameter with a nested class in this class?

By : user2176114
Date : October 14 2020, 02:22 PM
Hope that helps Well, you simply can't do that, and you've already pointed out why that is.
Thinking more about logic than about syntax, since the base class definition may very well differ depending on what its template argument is, and since the base class definition may very well affect the way TestInner works, you are attempting to create a circular dependency which is just not possible in our physical reality.
code :

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Using child class as a template parameter of a base class and as a nested name specifier

By : icom85
Date : March 29 2020, 07:55 AM
This might help you The solution was, as ildjarn pointed out, to add another level of indirection.
That is done by changing the test function to accept types:
code :
template <typename X, class U = void>
struct test {
    typedef U type;
    template<class Y=workerClass>
    typename test<decltype(&Y::fly)>::type 
    invoke2(Param<Fly>) {

    template<class Y=workerClass>
    typename test<decltype(&Y::swim)>::type 
    invoke2(Param<Swim>) {
class MyClass : public BaseClass<MyClass>
    void swim() {
        printf("Swimming like a fish!\n");

    /* void fly(); */

void testing() {
    MyClass foo;
    foo.invoke<Fly>(); /* No 'void fly()' in MyClass, calls the default handler */
    foo.invoke<Swim>(); /* Should print the swimming message */

Nested class as a template parameter of parent class in C++

By : mio188
Date : March 29 2020, 07:55 AM
Any of those help I think your problem is the the compiler doesn't know what the inner class looks like until it has defined the outer class and the outer class is defined with the inner class as a template parameter. I'm not 100% sure this can't be made to work. The CRTP is an example similar to this that is known to work.
Templates can be used to create inheritance hierarchies, but should not be use the in the definition of a hierarchy. If that sounds confusing, it's because it is. Inheritance and template classes don't mix well. Notice that even though CRTP uses inheritance and templates it does not use virtual functions.

gcc compiling error: member of nested class A in template class Table is not visible in nested friend class. Why?

By : simeng
Date : March 29 2020, 07:55 AM
it fixes the issue Within a template, member access must sometimes be preceded by an explicit this->, as in this case. You can make your code work this way:
code :
this->nEntry = 1;

Use nested class of templated class as template template parameter in C++

By : H.Amy
Date : March 29 2020, 07:55 AM
this one helps. In C++, I'd like to use a nested class inside a templated class as template template parameter. For non-nested classes the pattern is: , You may create an template alias:
code :
template <typename T>
using innerAA = typename A<T>::AA;
B<int, innerAA> b42;

Inheriting with default template parameter of nested class within template outer class

By : ankita moghe
Date : March 29 2020, 07:55 AM
hop of those help? Well, after posting I found the answer in this question. I'll leave it here in case it is useful for anyone else. When using the defaults, you still have to put <> at the end of the class name to turn it from the name of a template into the name of an instantiated class (per this answer to the above question). This compiles successfully:
code :
template<typename T>
class Outer {
  template<typename U = void>
  class Inner {
    Outer *outer_;
    Inner(Outer *outer): outer_(outer) {}
}; //Outer

typedef Outer<int> SpecializedOuter;

class SpecializedInner: public SpecializedOuter::Inner<> { 
    // without <void>, but with <> => OK
  SpecializedInner(SpecializedOuter *so)
    : Inner<>(so)     // without <void>, with <> => OK.  Plus, don't have to
  {}                  // re-specify `SpecializedOuter::`!
// vi: set ts=2 sts=2 sw=2 et ai: //
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