clang/test/SemaTemplate/generic-lambda.cpp

   1 // RUN: %clang_cc1 -std=c++20 -fsyntax-only -verify %s
   2
   3 // expected-no-diagnostics
   4
   5 template <class T, class U> constexpr bool is_same_v = false;
   6 template <class T> constexpr bool is_same_v<T, T> = true;
   7 template <class T, class U>
   8 concept is_same = is_same_v<T, U>;
   9
  10 template <class T> struct X {};
  11 template <class T, class U>
  12 concept C1 = is_same<T, X<U>>;
  13
  14 template <class T1> X<X<X<T1>>> t1() {
  15   return []<class T2>(T2) -> X<X<T2>> {
  16     struct S {
  17       static X<X<T2>> f() {
  18         return []<class T3>(T3) -> X<T3> {
  19           static_assert(is_same<T2, X<T1>>);
  20           static_assert(is_same<T3, X<T2>>);
  21           return X<T3>();
  22         }(X<T2>());
  23       }
  24     };
  25     return S::f();
  26   }(X<T1>());
  27 };
  28 template X<X<X<int>>> t1<int>();
  29
  30 #if 0 // FIXME: crashes
  31 template<class T1> auto t2() {
  32   return []<class T2>(T2) {
  33     struct S {
  34       static auto f() {
  35         return []<class T3>(T3) {
  36           static_assert(is_same<T2, X<T1>>);
  37           static_assert(is_same<T3, X<T2>>);
  38           return X<T3>();
  39         }(X<T2>());
  40       }
  41     };
  42     return S::f();
  43   }(X<T1>());
  44 };
  45 template auto t2<int>();
  46 static_assert(is_same<decltype(t2<int>()), X<X<X<int>>>>);
  47
  48 template<class T1> C1<X<X<T1>>> auto t3() {
  49   return []<C1<T1> T2>(T2) -> C1<X<T2>> auto {
  50     struct S {
  51       static auto f() {
  52         return []<C1<T2> T3>(T3) -> C1<T3> auto {
  53           return X<T3>();
  54         }(X<T2>());
  55       }
  56     };
  57     return S::f();
  58   }(X<T1>());
  59 };
  60 template C1<X<X<int>>> auto t3<int>();
  61 static_assert(is_same<decltype(t3<int>()), X<X<X<int>>>>);
  62 #endif