gcc/testsuite/g++.dg/cpp2a/constexpr-ref1.C

   1 // P2280R4 - Using unknown pointers and references in constant expressions
   2 // PR c++/106650
   3 // { dg-do compile { target c++20 } }
   4
   5 #include <typeinfo>
   6
   7 using size_t = decltype(sizeof(42));
   8
   9 template <typename T, size_t N>
  10 constexpr size_t array_size(T (&)[N]) {
  11   return N;
  12 }
  13
  14 void use_array(int const (&gold_medal_mel)[2]) {
  15   constexpr auto gold = array_size(gold_medal_mel);     // OK
  16 }
  17
  18 constexpr auto olympic_mile() {
  19   const int ledecky = 1500;
  20   return []{ return ledecky; };
  21 }
  22 static_assert(olympic_mile()() == 1500);                // OK
  23
  24 struct Swim {
  25   constexpr int phelps() { return 28; }
  26   virtual constexpr int lochte() { return 12; }
  27   int coughlin = 12;
  28 };
  29
  30 constexpr int how_many(Swim& swam) {
  31   Swim* p = &swam;
  32   return (p + 1 - 1)->phelps();
  33 }
  34
  35 void splash(Swim& swam) {
  36   static_assert(swam.phelps() == 28);           // OK
  37   static_assert((&swam)->phelps() == 28);       // OK
  38
  39   Swim* pswam = &swam;
  40   static_assert(pswam->phelps() == 28);         // { dg-error "non-constant|not usable" }
  41
  42   static_assert(how_many(swam) == 28);          // OK
  43   static_assert(Swim().lochte() == 12);         // OK
  44
  45   static_assert(swam.lochte() == 12);           // { dg-error "non-constant|not a constant" }
  46
  47   static_assert(swam.coughlin == 12);           // { dg-error "non-constant|not a constant" }
  48 }
  49
  50 extern Swim dc;
  51 extern Swim& trident;
  52
  53 constexpr auto& sandeno   = typeid(dc);         // OK, can only be typeid(Swim)
  54 constexpr auto& gallagher = typeid(trident);    // { dg-error "not a constant" }