field has incomplete type C++

I am trying to make class that has a member of type of it's enclosing class but I get an error saying field has incomplete type. here is an example

class List {
public:
        List (int element, List rest) {
                 _first = element;
                 _rest = rest;
         }
.
.
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}

Is there a way to fix this problem?

You haven't given us the complete definition of List, but I'm guessing from your description that you have something like:

class List
{
    ...
    List _rest;
};

Obviously, this is impossible. An object cannot contain a member of its own type, as this would lead to an infinite recursion!

Perhaps you want a member that is a pointer or a reference?

Use this:

'rest' should be a pointer to a List.