1 files changed, 137 insertions, 0 deletions
diff --git a/test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp b/test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp
new file mode 100644
index 000000000000..8f694cfd5eda
--- /dev/null
+++ b/test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp
@@ -0,0 +1,137 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// template <size_t I, class ...Args> void emplace(Args&&... args);
+
+#include <cassert>
+#include <string>
+#include <type_traits>
+#include <variant>
+
+#include "archetypes.hpp"
+#include "test_convertible.hpp"
+#include "test_macros.h"
+#include "variant_test_helpers.hpp"
+
+template <class Var, size_t I, class... Args>
+constexpr auto test_emplace_exists_imp(int) -> decltype(
+    std::declval<Var>().template emplace<I>(std::declval<Args>()...), true) {
+  return true;
+}
+
+template <class, size_t, class...>
+constexpr auto test_emplace_exists_imp(long) -> bool {
+  return false;
+}
+
+template <class Var, size_t I, class... Args> constexpr bool emplace_exists() {
+  return test_emplace_exists_imp<Var, I, Args...>(0);
+}
+
+void test_emplace_sfinae() {
+  {
+    using V = std::variant<int, void *, const void *, TestTypes::NoCtors>;
+    static_assert(emplace_exists<V, 0>(), "");
+    static_assert(emplace_exists<V, 0, int>(), "");
+    static_assert(!emplace_exists<V, 0, decltype(nullptr)>(),
+                  "cannot construct");
+    static_assert(emplace_exists<V, 1, decltype(nullptr)>(), "");
+    static_assert(emplace_exists<V, 1, int *>(), "");
+    static_assert(!emplace_exists<V, 1, const int *>(), "");
+    static_assert(!emplace_exists<V, 1, int>(), "cannot construct");
+    static_assert(emplace_exists<V, 2, const int *>(), "");
+    static_assert(emplace_exists<V, 2, int *>(), "");
+    static_assert(!emplace_exists<V, 3>(), "cannot construct");
+  }
+#if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
+  {
+    using V = std::variant<int, int &, const int &, int &&, TestTypes::NoCtors>;
+    static_assert(emplace_exists<V, 0>(), "");
+    static_assert(emplace_exists<V, 0, int>(), "");
+    static_assert(emplace_exists<V, 0, long long>(), "");
+    static_assert(!emplace_exists<V, 0, int, int>(), "too many args");
+    static_assert(emplace_exists<V, 1, int &>(), "");
+    static_assert(!emplace_exists<V, 1>(), "cannot default construct ref");
+    static_assert(!emplace_exists<V, 1, const int &>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 1, int &&>(), "cannot bind ref");
+    static_assert(emplace_exists<V, 2, int &>(), "");
+    static_assert(emplace_exists<V, 2, const int &>(), "");
+    static_assert(emplace_exists<V, 2, int &&>(), "");
+    static_assert(!emplace_exists<V, 2, void *>(),
+                  "not constructible from void*");
+    static_assert(emplace_exists<V, 3, int>(), "");
+    static_assert(!emplace_exists<V, 3, int &>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 3, const int &>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 3, const int &&>(), "cannot bind ref");
+    static_assert(!emplace_exists<V, 4>(), "no ctors");
+  }
+#endif
+}
+
+void test_basic() {
+  {
+    using V = std::variant<int>;
+    V v(42);
+    v.emplace<0>();
+    assert(std::get<0>(v) == 0);
+    v.emplace<0>(42);
+    assert(std::get<0>(v) == 42);
+  }
+  {
+    using V =
+        std::variant<int, long, const void *, TestTypes::NoCtors, std::string>;
+    const int x = 100;
+    V v(std::in_place_index<0>, -1);
+    // default emplace a value
+    v.emplace<1>();
+    assert(std::get<1>(v) == 0);
+    v.emplace<2>(&x);
+    assert(std::get<2>(v) == &x);
+    // emplace with multiple args
+    v.emplace<4>(3, 'a');
+    assert(std::get<4>(v) == "aaa");
+  }
+#if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
+  {
+    using V = std::variant<int, long, const int &, int &&, TestTypes::NoCtors,
+                           std::string>;
+    const int x = 100;
+    int y = 42;
+    int z = 43;
+    V v(std::in_place_index<0>, -1);
+    // default emplace a value
+    v.emplace<1>();
+    assert(std::get<1>(v) == 0);
+    // emplace a reference
+    v.emplace<2>(x);
+    assert(&std::get<2>(v) == &x);
+    // emplace an rvalue reference
+    v.emplace<3>(std::move(y));
+    assert(&std::get<3>(v) == &y);
+    // re-emplace a new reference over the active member
+    v.emplace<3>(std::move(z));
+    assert(&std::get<3>(v) == &z);
+    // emplace with multiple args
+    v.emplace<5>(3, 'a');
+    assert(std::get<5>(v) == "aaa");
+  }
+#endif
+}
+
+int main() {
+  test_basic();
+  test_emplace_sfinae();
+}