Re: TODO: egcs-g++

[Andi Kleen <ak at muc dot de>]

On Sun, Apr 11, 1999 at 10:40:03AM +0200, Jason Merrill wrote:
> Would someone explain to me what anonymous structs are good for?  It seems
> like a totally pointless extension.

It is a nice way to short cut the #define mazes one often sees, e.g.

struct bla { 
	// ...
	union { 
		struct { int a,b; } A;
		int c;
	} blub; 
}; 
#define bla_a blub.A.a
#define bla_b blub.A.b
#define bla_c bla.c

Another use would be "poor man's inheritance" in C:

struct node {
	struct node *prev, *next;
}; 
struct bla { 
	struct node;
	int val; 
}; 

Now you can walk the bla list directly via ->next and ->prev points,
without playing macro games, or having to type the error prone 
nd.prev/nd.next all the time (ok the cast is still ugly). 

I have seen these two situations very often in real world code.

They are also a nice symetry to anonymous unions in C++; I would guess
if you implement one it isn't that hard to implement the other (and
anonymous unions are already implemented in G++, but not in GCC) 

here was a C9x proposal from Ken Thompson that described the rationale
for it better than me, but I cannot find it on the super slow WG14 WWW
server ATM. The comitee did reject it for some reason though.

I think they would be useful, but of course the tradeoff between just
another extension and maintainability is up to the maintainers.

-Andi

-- 
This is like TV. I don't like TV.