c++ - How do I forward declare an inner class?

Question

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Answer 1

This is simply not possible. You cannot forward declare a nested structure outside the container. You can only forward declare it within the container.

You'll need to do one of the following

• Make the class non-nested
• Change your declaration order so that the nested class is fully defined first
• Create a common base class that can be both used in the function and implemented by the nested class.