clang/test/SemaTemplate/cxx1z-fold-expressions.cpp

   1 // RUN: %clang_cc1 -std=c++1z -verify %s
   2 // RUN: %clang_cc1 -std=c++2a -verify %s
   3
   4 template<typename ...T> constexpr auto sum(T ...t) { return (... + t); }
   5 template<typename ...T> constexpr auto product(T ...t) { return (t * ...); }
   6 template<typename ...T> constexpr auto all(T ...t) { return (true && ... && t); }
   7 template<typename ...T> constexpr auto dumb(T ...t) { return (false && ... && t); }
   8
   9 static_assert(sum(1, 2, 3, 4, 5) == 15);
  10 static_assert(product(1, 2, 3, 4, 5) == 120);
  11 static_assert(!all(true, true, false, true, false));
  12 static_assert(all(true, true, true, true, true));
  13 static_assert(!dumb(true, true, true, true, true));
  14
  15 struct S {
  16   int a, b, c, d, e;
  17 };
  18 template<typename ...T> constexpr auto increment_all(T &...t) {
  19   (++t, ...);
  20 }
  21 constexpr bool check() {
  22   S s = { 1, 2, 3, 4, 5 };
  23   increment_all(s.a, s.b, s.c, s.d, s.e);
  24   return s.a == 2 && s.b == 3 && s.c == 4 && s.d == 5 && s.e == 6;
  25 }
  26 static_assert(check());
  27
  28 template<int ...N> void empty() {
  29   static_assert((N || ...) == false);
  30   static_assert((N && ...) == true);
  31   (N, ...);
  32 }
  33 template void empty<>();
  34
  35 // An empty fold-expression isn't a null pointer just because it's an integer
  36 // with value 0. (This is no longer an issue since empty pack expansions don't
  37 // produce integers any more.)
  38 template<int ...N> void null_ptr() {
  39   void *p = (N || ...); // expected-error {{rvalue of type 'bool'}}
  40   void *q = (N , ...); // expected-error {{rvalue of type 'void'}}
  41 }
  42 template void null_ptr<>(); // expected-note {{in instantiation of}}
  43
  44 template<int ...N> void bad_empty() {
  45   (N + ...); // expected-error {{empty expansion for operator '+' with no fallback}}
  46   (N * ...); // expected-error {{empty expansion for operator '*' with no fallback}}
  47   (N | ...); // expected-error {{empty expansion for operator '|' with no fallback}}
  48   (N & ...); // expected-error {{empty expansion for operator '&' with no fallback}}
  49   (N - ...); // expected-error {{empty expansion for operator '-' with no fallback}}
  50   (N / ...); // expected-error {{empty expansion for operator '/' with no fallback}}
  51   (N % ...); // expected-error {{empty expansion for operator '%' with no fallback}}
  52   (N = ...); // expected-error {{empty expansion for operator '=' with no fallback}}
  53 }
  54 template void bad_empty<>(); // expected-note {{in instantiation of}}
  55
  56 template<int ...N> void empty_with_base() {
  57   extern int k;
  58   (k = ... = N); // expected-warning{{unused}}
  59
  60   void (k = ... = N); // expected-error {{expected ')'}} expected-note {{to match}}
  61   void ((k = ... = N));
  62   (void) (k = ... = N);
  63 }
  64 template void empty_with_base<>(); // expected-note {{in instantiation of}}
  65 template void empty_with_base<1>();
  66
  67 struct A {
  68   struct B {
  69     struct C {
  70       struct D {
  71         int e;
  72       } d;
  73     } c;
  74   } b;
  75 } a;
  76 template<typename T, typename ...Ts> constexpr decltype(auto) apply(T &t, Ts ...ts) {
  77   return (t.*....*ts);
  78 }
  79 static_assert(&apply(a, &A::b, &A::B::c, &A::B::C::d, &A::B::C::D::e) == &a.b.c.d.e);
  80
  81 #if __cplusplus > 201703L
  82 // The <=> operator is unique among binary operators in not being a
  83 // fold-operator.
  84 // FIXME: This diagnostic is not great.
  85 template<typename ...T> constexpr auto spaceship1(T ...t) { return (t <=> ...); } // expected-error {{expected expression}}
  86 template<typename ...T> constexpr auto spaceship2(T ...t) { return (... <=> t); } // expected-error {{expected expression}}
  87 template<typename ...T> constexpr auto spaceship3(T ...t) { return (t <=> ... <=> 0); } // expected-error {{expected expression}}
  88 #endif
  89
  90 // The GNU binary conditional operator ?: is not recognized as a fold-operator.
  91 // FIXME: Why not? This seems like it would be useful.
  92 template<typename ...T> constexpr auto binary_conditional1(T ...t) { return (t ?: ...); } // expected-error {{expected expression}}
  93 template<typename ...T> constexpr auto binary_conditional2(T ...t) { return (... ?: t); } // expected-error {{expected expression}}
  94 template<typename ...T> constexpr auto binary_conditional3(T ...t) { return (t ?: ... ?: 0); } // expected-error {{expected expression}}
  95
  96 namespace PR41845 {
  97   template <int I> struct Constant {};
  98
  99   template <int... Is> struct Sum {
 100     template <int... Js> using type = Constant<((Is + Js) + ... + 0)>; // expected-error {{pack expansion contains parameter pack 'Js' that has a different length (1 vs. 2) from outer parameter packs}}
 101   };
 102
 103   Sum<1>::type<1, 2> x; // expected-note {{instantiation of}}
 104 }
 105
 106 namespace PR30738 {
 107   namespace N {
 108     struct S {};
 109   }
 110
 111   namespace T {
 112     void operator+(N::S, N::S) {}
 113     template<typename ...Ts> void f() { (Ts{} + ...); }
 114   }
 115
 116   void g() { T::f<N::S, N::S>(); }
 117
 118   template<typename T, typename ...U> auto h(U ...v) {
 119     T operator+(T, T); // expected-note {{candidate}}
 120     return (v + ...); // expected-error {{invalid operands}}
 121   }
 122   int test_h1 = h<N::S>(1, 2, 3);
 123   N::S test_h2 = h<N::S>(N::S(), N::S(), N::S());
 124   int test_h3 = h<struct X>(1, 2, 3);
 125   N::S test_h4 = h<struct X>(N::S(), N::S(), N::S()); // expected-note {{instantiation of}}
 126 }
 127
 128 namespace GH67395 {
 129 template <typename>
 130 bool f();
 131
 132 template <typename... T>
 133 void g(bool = (f<T>() || ...));
 134 }