🚀 go-pugleaf

Henry Baker (henry.baker@wem.org) wrote:

: Suppose I have the following nested class:

: struct pair
: {struct pair_rep
:  {pair car,cdr;};    // inner class has member of outer class.
:  pair_rep *rep;};

: I understand the rule saying that a class cannot be a member of itself
: [Stroustrup#2, page 545] (Bertrand Russell is now spinning in his grave ;-),
: but I'm having trouble understanding why a _nested_ class cannot have a
: member
: of the outer class being defined.  This is especially irritating, since the
: above is capable of being rewritten as [Stroustrup#2, page 645]:

: struct pair
: {struct pair_rep;
:  pair_rep *rep;};

: struct pair::pair_rep
: {pair car,cdr;};

: Are compiler writers just being lazy, or what??


It appears that the struct type  pair  is not yet defined at the point
where it is used to delcare car and cdr.  (Note that sizeof(pair) will 
not be known for another two lines.)  

In the revised version, when the struct type  pair  is used to declare
car and cdr, it is already known that pairs consist of a single member
called rep, which points to a structure of a thus-far undefined type
called pair_rep.


Tom Payne (thp@cs.ucr.edu)