[flang-commits] [flang] [libcxx] [lldb] [clang] [compiler-rt] [libc] [clang-tools-extra] [llvm] [libc++][variant] P2637R3: Member `visit` (`std::variant`) (PR #76447)
Hristo Hristov via flang-commits
flang-commits at lists.llvm.org
Sun Dec 31 00:39:30 PST 2023
================
@@ -0,0 +1,268 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+
+// <variant>
+
+// class variant;
+
+// template<class Self, class Visitor>
+// constexpr decltype(auto) visit(this Self&&, Visitor&&); // since C++26
+
+#include <cassert>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <variant>
+
+#include "test_macros.h"
+#include "variant_test_helpers.h"
+
+void test_call_operator_forwarding() {
+ using Fn = ForwardingCallObject;
+ Fn obj{};
+ const Fn& cobj = obj;
+
+ { // test call operator forwarding - no variant
+ // non-member
+ {
+ std::visit(obj);
+ assert(Fn::check_call<>(CT_NonConst | CT_LValue));
+ std::visit(cobj);
+ assert(Fn::check_call<>(CT_Const | CT_LValue));
+ std::visit(std::move(obj));
+ assert(Fn::check_call<>(CT_NonConst | CT_RValue));
+ std::visit(std::move(cobj));
+ assert(Fn::check_call<>(CT_Const | CT_RValue));
+ }
+ }
+ { // test call operator forwarding - single variant, single arg
+ using V = std::variant<int>;
+ V v(42);
+
+ v.visit(obj);
+ assert(Fn::check_call<int&>(CT_NonConst | CT_LValue));
+ v.visit(cobj);
+ assert(Fn::check_call<int&>(CT_Const | CT_LValue));
+ v.visit(std::move(obj));
+ assert(Fn::check_call<int&>(CT_NonConst | CT_RValue));
+ v.visit(std::move(cobj));
+ assert(Fn::check_call<int&>(CT_Const | CT_RValue));
+ }
+ { // test call operator forwarding - single variant, multi arg
+ using V = std::variant<int, long, double>;
+ V v(42L);
+
+ v.visit(obj);
+ assert(Fn::check_call<long&>(CT_NonConst | CT_LValue));
+ v.visit(cobj);
+ assert(Fn::check_call<long&>(CT_Const | CT_LValue));
+ v.visit(std::move(obj));
+ assert(Fn::check_call<long&>(CT_NonConst | CT_RValue));
+ v.visit(std::move(cobj));
+ assert(Fn::check_call<long&>(CT_Const | CT_RValue));
+ }
+}
+
+// Applies to non-member `std::visit` only.
+void test_argument_forwarding() {
+ using Fn = ForwardingCallObject;
+ Fn obj{};
+ const auto val = CT_LValue | CT_NonConst;
+
+ { // single argument - value type
+ using V = std::variant<int>;
+ V v(42);
+ const V& cv = v;
+
+ v.visit(obj);
+ assert(Fn::check_call<int&>(val));
+ cv.visit(obj);
+ assert(Fn::check_call<const int&>(val));
+ std::move(v).visit(obj);
+ assert(Fn::check_call<int&&>(val));
+ std::move(cv).visit(obj);
+ assert(Fn::check_call<const int&&>(val));
+ }
+#if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
+ { // single argument - lvalue reference
+ using V = std::variant<int&>;
+ int x = 42;
+ V v(x);
+ const V& cv = v;
+
+ v.visit(obj);
+ assert(Fn::check_call<int&>(val));
+ cv.visit(obj);
+ assert(Fn::check_call<int&>(val));
+ std::move(v).visit(obj);
+ assert(Fn::check_call<int&>(val));
+ std::move(cv).visit(obj);
+ assert(Fn::check_call<int&>(val));
+ assert(false);
+ }
+ { // single argument - rvalue reference
+ using V = std::variant<int&&>;
+ int x = 42;
+ V v(std::move(x));
+ const V& cv = v;
+
+ v.visit(obj);
+ assert(Fn::check_call<int&>(val));
+ cvstd::visit(obj);
+ assert(Fn::check_call<int&>(val));
+ std::move(v).visit(obj);
+ assert(Fn::check_call<int&&>(val));
+ std::move(cv).visit(obj);
+ assert(Fn::check_call<int&&>(val));
+ }
+#endif
+}
+
+void test_return_type() {
+ using Fn = ForwardingCallObject;
+ Fn obj{};
+ const Fn& cobj = obj;
+
+ { // test call operator forwarding - single variant, single arg
+ using V = std::variant<int>;
+ V v(42);
+
+ static_assert(std::is_same_v<decltype(v.visit(obj)), Fn&>);
+ static_assert(std::is_same_v<decltype(v.visit(cobj)), const Fn&>);
+ static_assert(std::is_same_v<decltype(v.visit(std::move(obj))), Fn&&>);
+ static_assert(std::is_same_v<decltype(v.visit(std::move(cobj))), const Fn&&>);
+ }
+ { // test call operator forwarding - single variant, multi arg
+ using V = std::variant<int, long, double>;
+ V v(42L);
+
+ static_assert(std::is_same_v<decltype(v.visit(obj)), Fn&>);
+ static_assert(std::is_same_v<decltype(v.visit(cobj)), const Fn&>);
+ static_assert(std::is_same_v<decltype(v.visit(std::move(obj))), Fn&&>);
+ static_assert(std::is_same_v<decltype(v.visit(std::move(cobj))), const Fn&&>);
+ }
+}
+
+void test_constexpr() {
+ constexpr ReturnFirst obj{};
+
+ {
+ using V = std::variant<int>;
+ constexpr V v(42);
+
+ static_assert(v.visit(obj) == 42);
+ }
+ {
+ using V = std::variant<short, long, char>;
+ constexpr V v(42L);
+
+ static_assert(v.visit(obj) == 42);
+ }
+}
+
+void test_exceptions() {
+#ifndef TEST_HAS_NO_EXCEPTIONS
+ ReturnArity obj{};
+
+ auto test = [&](auto&& v) {
+ try {
+ v.visit(obj);
+ } catch (const std::bad_variant_access&) {
+ return true;
+ } catch (...) {
+ }
+ return false;
+ };
+
+ {
+ using V = std::variant<int, MakeEmptyT>;
+ V v;
+ makeEmpty(v);
+
+ assert(test(v));
+ }
+#endif
+}
+
+// See https://llvm.org/PR31916
+void test_caller_accepts_nonconst() {
+ struct A {};
+ struct Visitor {
+ void operator()(A&) {}
+ };
+ std::variant<A> v;
+
+ v.visit(Visitor{});
+}
+
+struct MyVariant : std::variant<short, long, float> {};
+
+namespace std {
+template <std::size_t Index>
+void get(const MyVariant&) {
+ assert(false);
+}
+} // namespace std
+
+void test_derived_from_variant() {
+ auto v1 = MyVariant{42};
+ const auto cv1 = MyVariant{142};
+
+ v1.visit([](auto x) { assert(x == 42); });
+ cv1.visit([](auto x) { assert(x == 142); });
+ MyVariant{-1.25f}.visit([](auto x) { assert(x == -1.25f); });
+ std::move(v1).visit([](auto x) { assert(x == 42); });
+ std::move(cv1).visit([](auto x) { assert(x == 142); });
+
+ // Check that visit does not take index nor valueless_by_exception members from the base class.
+ struct EvilVariantBase {
+ int index;
+ char valueless_by_exception;
+ };
+
+ struct EvilVariant1 : std::variant<int, long, double>, std::tuple<int>, EvilVariantBase {
+ using std::variant<int, long, double>::variant;
+ };
+
+ EvilVariant1{12}.visit([](auto x) { assert(x == 12); });
+ EvilVariant1{12.3}.visit([](auto x) { assert(x == 12.3); });
+
+ // Check that visit unambiguously picks the variant, even if the other base has __impl member.
+ struct ImplVariantBase {
+ struct Callable {
+ bool operator()() const {
+ assert(false);
+ return false;
+ }
+ };
+
+ Callable __impl;
+ };
+
+ struct EvilVariant2 : std::variant<int, long, double>, ImplVariantBase {
+ using std::variant<int, long, double>::variant;
+ };
+
+ EvilVariant2{12}.visit([](auto x) { assert(x == 12); });
+ EvilVariant2{12.3}.visit([](auto x) { assert(x == 12.3); });
+}
+
+int main(int, char**) {
+ test_call_operator_forwarding();
+ test_argument_forwarding();
+ test_return_type();
+ test_constexpr();
----------------
H-G-Hristov wrote:
My reasoning was to keep the member visit tests as close as possible to the original non-member function ones, for easier matching/reviewing as they are expected to produce the same results. I kept the structure and the names. Initially I wrote the tests in the same file before splitting them into two separate.
https://github.com/llvm/llvm-project/pull/76447
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