clang/test/SemaCXX/libstdcxx_libcxx_less_hack.cpp

   1 // This is a test for a hack in Clang that works around a problem introduced by
   2 // DR583: it's no longer possible to compare a pointer against nullptr_t, but
   3 // we still want to permit those comparisons within less<> and friends.
   4
   5 // RUN: %clang_cc1 -verify %s -std=c++14
   6
   7 namespace std {
   8   template<typename T = void> struct less {};
   9   template<typename T = void> struct less_equal {};
  10   template<typename T = void> struct greater {};
  11   template<typename T = void> struct greater_equal {};
  12
  13   template<> struct less<> {
  14     template <class T1, class T2>
  15     auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t < u))
  16         -> decltype(t < u) {
  17       return t < u;
  18     }
  19   };
  20
  21   template<> struct less_equal<> {
  22     template <class T1, class T2>
  23     auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t <= u))
  24         -> decltype(t <= u) {
  25       return t <= u;
  26     }
  27   };
  28
  29   template<> struct greater<> {
  30     template <class T1, class T2>
  31     auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t > u))
  32         -> decltype(t > u) {
  33       return t > u;
  34     }
  35   };
  36
  37   template<> struct greater_equal<> {
  38     template <class T1, class T2>
  39     auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t >= u))
  40         -> decltype(t >= u) {
  41       return t >= u;
  42     }
  43   };
  44
  45   template<typename = void> struct unrelated;
  46   template<> struct unrelated<> {
  47     template <class T1, class T2>
  48     auto operator()(T1 &&t, T2 &&u) const noexcept(noexcept(t < u)) // expected-note {{substitution failure}}
  49         -> decltype(t < u) {
  50       return t < u;
  51     }
  52   };
  53 };
  54
  55 void test(int *p) {
  56   using namespace std;
  57   less<>()(p, nullptr);
  58   less<>()(nullptr, p);
  59   less_equal<>()(p, nullptr);
  60   less_equal<>()(nullptr, p);
  61   greater<>()(p, nullptr);
  62   greater<>()(nullptr, p);
  63   greater_equal<>()(p, nullptr);
  64   greater_equal<>()(nullptr, p);
  65
  66   unrelated<>()(p, nullptr); // expected-error {{no matching function}}
  67 }