clang/test/SemaCXX/lambda-pack-expansion.cpp

// RUN: %clang_cc1 -std=c++20 -Wno-unused-value -fsyntax-only -verify %s

namespace GH49266 {
struct X {
  X() = default;
  X(X const&) = delete; // expected-note {{'X' has been explicitly marked deleted here}}
};

void take_by_copy(auto &...args) {
  [...args = args] {}(); // expected-error {{call to deleted constructor}}
}

void take_by_ref(auto &...args) {
  [&...args = args] {}(); // args is passed by reference and not copied.
}

void foo() {
  X x;
  take_by_copy(x); // expected-note {{in instantiation of function template specialization}}
  take_by_ref(x);
}
}

namespace GH48937 {

template <typename... Ts>
consteval int f(Ts... ts) {
  return ([]<Ts a = 42>(){ return a;}, ...)();
}

static_assert(f(0, 42) == 42);

template <typename Ts>
int g(Ts ts) {
  return ([]<Ts a = 42>(){ return a;}, ...)();  // expected-error {{pack expansion does not contain any unexpanded parameter packs}}
}

template <typename... Ts>
int h(Ts... ts) {
  return ([]<Ts a = 42>(){ return a;})();  // expected-error {{expression contains unexpanded parameter pack 'Ts'}}
}

}

namespace GH63677 {

template<typename>
void f() {
  []<typename... Ts>() -> void {
    [...us = Ts{}]{
      (Ts(us), ...);
    };
  }.template operator()<int, int>();
}

template void f<int>();

template <class>
inline constexpr auto fun =
  []<class... Ts>(Ts... ts) {
    return [... us = (Ts&&) ts]<class Fun>(Fun&& fn) mutable {
      return static_cast<Fun&&>(fn)(static_cast<Ts&&>(us)...);
    };
  };

void f() {
  [[maybe_unused]] auto s = fun<int>(1, 2, 3, 4);
}

}