RE: [C++0x] implementing forward declarations for enums

["Hargett, Matt" <matt dot hargett at bluecoat dot com>]

I just wanted to say thanks for implementing this.

Being able to forward declare enums will make dependency breaking in legacy code much easier in many real-world cases. 

Thanks again!

-----Original Message-----
From: gcc-owner@gcc.gnu.org [mailto:gcc-owner@gcc.gnu.org] On Behalf Of Rodrigo Rivas
Sent: Monday, September 20, 2010 6:58 AM
To: gcc@gcc.gnu.org
Subject: [C++0x] implementing forward declarations for enums

Hello all.

This patch tries to implement the C++0x featue "Forward declarations for enums" aka "opaque enum declarations":
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2764.pdf

Please note that this is a WIP, and as such lacks formatting, comments, testcases, etc.

Except for the things noted below, I think it works pretty well.

TODOs
1
A enum declaration should fail if adds a list of constants and it already have one. I check it with "TYPE_VALUES (type)", but this is incorrect because an empty list will not be seen.
So, the current patch will accept incorrect code like:
enum class Foo { };
enum class Foo { A, B, C};
I think that a new flag is needed for ENUMERAL_TYPE, but I don't know which one.

2
I am calling "finish_enum" several types, for each of the opaque declarations until it gets a list of constants. It doesn't seem to cause problems except with the debug information. With default flags and everything, gdb sees only the first declaration:
enum class Foo;
enum class Foo {A, B, C}
Foo f;

(gdb) ptype f;
enum Foo {}

I don't see an easy way to solve it...

3
I don't like very much the added parameter to the "start_enum"
function, but I don't see how to do it without breaking existing code.

Comments are most welcomed.

Regards.
Rodrigo