bug in stl_function.h

[Levente Farkas]

hi,
_Identity, _Select1st and _Select2nd should have to patch with the 
attachment in order to work with both const AND non-const pair.
the "feature" that operator() is not always return with result_type
is not too nice (although I understand sri's points about the original 
version), but it is not correct without the modification.

ps. anyways this const correctness is the biggest weekness of the standard.

 -- lfarkas
 "The only thing worse than not knowing the truth is
  ruining the bliss of ignorance."
*** stl_function.h-ori	Wed Apr 05 11:50:52 2000
--- stl_function.h	Wed Apr 05 11:51:46 2000
***************
*** 325,330 ****
--- 325,331 ----
  // identity is an extensions: it is not part of the standard.
  template <class _Tp>
  struct _Identity : public unary_function<_Tp,_Tp> {
+   _Tp& operator()(_Tp& __x) const { return __x; }
    const _Tp& operator()(const _Tp& __x) const { return __x; }
  };
  
***************
*** 333,338 ****
--- 334,342 ----
  // select1st and select2nd are extensions: they are not part of the standard.
  template <class _Pair>
  struct _Select1st : public unary_function<_Pair, typename _Pair::first_type> {
+   typename _Pair::first_type& operator()(_Pair& __x) const {
+     return __x.first;
+   }
    const typename _Pair::first_type& operator()(const _Pair& __x) const {
      return __x.first;
    }
***************
*** 341,346 ****
--- 345,353 ----
  template <class _Pair>
  struct _Select2nd : public unary_function<_Pair, typename _Pair::second_type>
  {
+   typename _Pair::second_type& operator()(_Pair& __x) const {
+     return __x.second;
+   }
    const typename _Pair::second_type& operator()(const _Pair& __x) const {
      return __x.second;
    }