clang/test/CXX/temp/temp.fct.spec/temp.deduct/temp.deduct.conv/p5.cpp

   1 // RUN: %clang_cc1 -std=c++1z -verify %s
   2
   3 template<typename T, bool B> using Fn = T () noexcept(B);
   4
   5 // - If the original A is a function pointer type, A can be "pointer to
   6 //   function" even if the deduced A is "pointer to noexcept function".
   7 struct A {
   8   template<typename T> operator Fn<T, false>*(); // expected-note {{candidate}}
   9 };
  10 struct B {
  11   template<typename T> operator Fn<T, true>*();
  12 };
  13 void (*p1)() = A();
  14 void (*p2)() = B();
  15 void (*p3)() noexcept = A(); // expected-error {{no viable conversion}}
  16 void (*p4)() noexcept = B();
  17
  18 // - If the original A is a pointer to member function type, A can be "pointer
  19 //   to member of type function" even if the deduced A is "pointer to member of
  20 //   type noexcept function".
  21 struct C {
  22   template<typename T> operator Fn<T, false> A::*(); // expected-note {{candidate}}
  23 };
  24 struct D {
  25   template<typename T> operator Fn<T, true> A::*();
  26 };
  27 void (A::*q1)() = C();
  28 void (A::*q2)() = D();
  29 void (A::*q3)() noexcept = C(); // expected-error {{no viable conversion}}
  30 void (A::*q4)() noexcept = D();
  31
  32 // There is no corresponding rule for references.
  33 // FIXME: This seems like a defect.
  34 // FIXME: We don't actually implement the final check for equal types at all!
  35 // Instead, we handle the matching via [over.ics.user]p3:
  36 //   "If the user-defined conversion is specified by a specialization of a
  37 //   conversion function template, the second standard conversion sequence
  38 //   shall have exact match rank."
  39 // Note that this *does* allow discarding noexcept, since that conversion has
  40 // Exact Match rank.
  41 struct E {
  42   template<typename T> operator Fn<T, false>&(); // expected-note {{candidate}}
  43 };
  44 struct F {
  45   template<typename T> operator Fn<T, true>&();
  46 };
  47 void (&r1)() = E();
  48 void (&r2)() = F();
  49 void (&r3)() noexcept = E(); // expected-error {{no viable conversion}}
  50 void (&r4)() noexcept = F();
  51
  52 // FIXME: We reject this for entirely the wrong reason. We incorrectly succeed
  53 // in deducing T = void, U = G::B, and only fail due to [over.ics.user]p3.
  54 struct G {
  55   template<typename, typename> struct A {};
  56   template<typename U> struct A<U, int> : A<U, void> {};
  57   struct B { typedef int type; };
  58
  59   template<typename T, typename U = B> operator A<T, typename U::type> *(); // expected-note {{candidate function [with T = void, U = G::B]}}
  60 };
  61 G::A<void, void> *g = G(); // expected-error {{no viable conversion}}