LessThanComparable requirement overspecified?

[scott snyder <snyder at fnal dot gov>]

hi -

I noticed that the latest update of the `STL' part of libstdc++
contains code to enforce the requirements on template parameters.
This is quite useful --- i've already found several instances in my
code where i was violating the spec.

However, there are some places where the new code seems to be overspecifying
the requirements --- making demands not required by the C++ standard ---
thus causing code that i believe to be legal to fail to compile.

Here is one example:

-----------------------------------------------------------------------
#include <algorithm>

struct foo {};

bool operator== (const foo&, const foo&);
bool operator< (const foo&, const foo&);

void bar (foo* a, foo* b, foo& x)
{
  foo* c = std::lower_bound (a, b, x);
}

-----------------------------------------------------------------------

When i try to compile this, i get:

/usr/local/egcs/include/g++-v3/bits/concept_checks.h: In function `_Type
_STL_ERROR::__less_than_comparable_requirement_violation (_Type, _Type) [with _Type = foo]':
/usr/local/egcs/include/g++-v3/bits/concept_checks.h:560:   instantiated from `_LessThanComparable_concept_specification<_Type>::_LessThanComparable_requirement_violation (_Type) [with _Type = foo]'
/usr/local/egcs/include/g++-v3/bits/stl_algo.h:1945:   instantiated from `std::lower_bound (_ForwardIter, _ForwardIter, const _Tp &) [with _ForwardIter = foo *, _Tp = foo]'
x.cc:10:   instantiated from here
/usr/local/egcs/include/g++-v3/bits/concept_checks.h:396: no match for `foo & >= foo &'
/usr/local/egcs/include/g++-v3/bits/concept_checks.h:396: no match for `foo & <= foo &'
/usr/local/egcs/include/g++-v3/bits/concept_checks.h:396: no match for `foo & > foo &'


If i look at what __less_than_comparable_requirement is actually requiring:

    if (__a < __b || __a > __b || __a <= __b || __a >= __b) return __a;

i.e., it requires the full suite of four inequality comparisons to be
present, not just `<'.

The requirement in the standard is that the type be LessThanComparable.
According to 20.1.2, this requires only a `<' relation --- so i think
that the code above is correct.

This patch gets rid of the extra requirements, and allows the above
example to compile.

2000-06-29  scott snyder  <snyder@fnal.gov>

	* bits/concept_checks.h
	(__less_then_comparable_requirement_violation): Only check for <.

Index: concept_checks.h
===================================================================
RCS file: /cvs/gcc/egcs/libstdc++-v3/bits/concept_checks.h,v
retrieving revision 1.1
diff -u -p -c -p -r1.1 concept_checks.h
*** concept_checks.h	2000/06/27 23:08:37	1.1
--- concept_checks.h	2000/06/29 21:58:32
*************** struct _STL_ERROR {
*** 393,399 ****
    template <class _Type>
    static _Type
    __less_than_comparable_requirement_violation(_Type __a, _Type __b) {
!     if (__a < __b || __a > __b || __a <= __b || __a >= __b) return __a;
      return __b;
    }
    template <class _Type>
--- 393,399 ----
    template <class _Type>
    static _Type
    __less_than_comparable_requirement_violation(_Type __a, _Type __b) {
!     if (__a < __b) return __a;
      return __b;
    }
    template <class _Type>