Re: libstdc++/4623: correct uses of _Bool in type-traits.h & instantiations

Re: libstdc++/4623: correct uses of _Bool in type-traits.h & instantiations

[bkoz]

Synopsis: correct uses of _Bool in type-traits.h & instantiations

State-Changed-From-To: open->closed
State-Changed-By: bkoz
State-Changed-When: Thu Oct 25 22:58:17 2001
State-Changed-Why:
    Fixed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&pr=4623&database=gcc

libstdc++/4623: correct uses of _Bool in type-traits.h & instantiations

[brendan]

>Number:         4623
>Category:       libstdc++
>Synopsis:       correct uses of _Bool in type-traits.h & instantiations
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Oct 19 14:56:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Brendan Kehoe
>Release:        CVS tree
>Organization:
>Environment:

>Description:
In type-traits.h, it creates an internal template named `_Bool', in order to make two typedefs `__true_type' and `__false_type'.  While the ISO C++ standard doesn't make any mention of `_Bool', the ISO C99 C standard does reserve `_Bool' in $6.7.2.

This can become a problem if a source file includes <stdbool.h> and something bringing in type_traits.h.  This wasn't a problem when most people used gcc 2.95.x, but now that gcc 3.x is in play, it can cause unexpected headaches.

One workaround in the past has been to add `#undef _Bool' just before the template definition in type_traits.h.   But this is not the requisite long-term fix.

I believe there are few if any examples of user code that actually make use of the `_Bool' template type that was made in type_traits.h.  However there will be an increasing number of platforms whose system headers may make use of <stdbool.h> in some way, which will produce unexpected compile-time errors for users without a suitable change.

>How-To-Repeat:
A test containing nothing but:

  #include <stdbool.h>
  #include <string>

will produce an error like


/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.1/include/g++/bits/type_traits.h:86: 
error: type
   specifier `bool' not allowed after struct or class

along with a good number of others afterwards.
>Fix:
The enclosed patch modifies the `_Bool' template to instead be named `__Boolean', and adjusts the two typedefs that use it.  In particular, we now have two leading underscores instead of one, to make it obvious that this is a type for an implementation and not something intended for user code.

It also goes into string-inst.cc and misc-inst.cc, and makes them use the two typedefs instead of the underlying template type.  That way if any future implementation change is required after this `__Boolean' change, it can be done without requiring spurious source changes.
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="diffs-bool.txt"
Content-Disposition: inline; filename="diffs-bool.txt"

2001-10-16  Brendan Kehoe  <brendan@zen.org>

	* bits/type_traits.h (__Boolean): Renamed template from _Bool.
	(__true_type, __false_type): Change usage.
	* src/string-inst.cc (__destroy_aux): Change third parm to be
	__false_type instead of _Bool<false>.
	* src/misc-inst.cc (__uninitialized_fill_n_aux,
	__uninitialized_copy_aux): Likewise.


*** include/bits/type_traits.h.~1~	Sun Jul  1 14:56:51 2001
--- include/bits/type_traits.h	Tue Oct 16 08:51:05 2001
*************** template <class _Tp> inline void copy(_T
*** 83,90 ****
  */
  
! 
! template <bool _Truth> struct _Bool {};
! typedef _Bool<true>  __true_type;
! typedef _Bool<false> __false_type;
  
  template <class _Tp>
--- 83,93 ----
  */
  
! // Note that we must use an internal name of __Boolean here, since the
! // identifier of _Bool, as we'd used in the past, is in fact reserved
! // by the C99 standard ($6.7.2).  As such, we'd introduce headaches if
! // someone happens to include <stdbool.h> along with this file.
! template <bool _Truth> struct __Boolean {};
! typedef __Boolean<true>  __true_type;
! typedef __Boolean<false> __false_type;
  
  template <class _Tp>
*** src/string-inst.cc.~1~	Wed Aug 29 23:22:35 2001
--- src/string-inst.cc	Tue Oct 16 08:47:08 2001
*************** namespace std 
*** 103,106 ****
    template
      void
!     __destroy_aux<S*>(S*, S*, _Bool<false>);
  } // namespace std
--- 103,106 ----
    template
      void
!     __destroy_aux<S*>(S*, S*, __false_type);
  } // namespace std
*** src/misc-inst.cc.~1~	Sun Mar 25 15:48:35 2001
--- src/misc-inst.cc	Tue Oct 16 08:54:43 2001
*************** namespace std
*** 234,238 ****
      string* 
      __uninitialized_fill_n_aux<string*, size_t, string>
!     (string*, size_t, string const &, _Bool<false>);
  
    template 
--- 234,238 ----
      string* 
      __uninitialized_fill_n_aux<string*, size_t, string>
!     (string*, size_t, string const &, __false_type);
  
    template 
*************** namespace std
*** 240,244 ****
      __uninitialized_copy_aux<vector<string>::const_iterator, string *>
      (vector<string>::const_iterator, vector<string>::const_iterator, 
!      string*, _Bool<false>);
  
    template
--- 240,244 ----
      __uninitialized_copy_aux<vector<string>::const_iterator, string *>
      (vector<string>::const_iterator, vector<string>::const_iterator, 
!      string*, __false_type);
  
    template