1//===- DenseMapInfoVariant.h - Type traits for DenseMap<variant> *- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file defines DenseMapInfo traits for DenseMap<std::variant<Ts...>>.
11///
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_DENSEMAPINFOVARIANT_H
15#define LLVM_ADT_DENSEMAPINFOVARIANT_H
16
17#include "llvm/ADT/DenseMapInfo.h"
18#include <utility>
19#include <variant>
20
21namespace llvm {
22
23// Provide DenseMapInfo for variants whose all alternatives have DenseMapInfo.
24template <typename... Ts> struct DenseMapInfo<std::variant<Ts...>> {
25 using Variant = std::variant<Ts...>;
26 using FirstT = std::variant_alternative_t<0, Variant>;
27
28 static inline Variant getEmptyKey() {
29 return Variant(std::in_place_index<0>, DenseMapInfo<FirstT>::getEmptyKey());
30 }
31
32 static inline Variant getTombstoneKey() {
33 return Variant(std::in_place_index<0>,
34 DenseMapInfo<FirstT>::getTombstoneKey());
35 }
36
37 static unsigned getHashValue(const Variant &Val) {
38 return std::visit(
39 [&Val](auto &&Alternative) {
40 using T = std::decay_t<decltype(Alternative)>;
41 // Include index in hash to make sure same value as different
42 // alternatives don't collide.
43 return DenseMapInfo<std::pair<size_t, T>>::getHashValuePiecewise(
44 Val.index(), Alternative);
45 },
46 Val);
47 }
48
49 static bool isEqual(const Variant &LHS, const Variant &RHS) {
50 if (LHS.index() != RHS.index())
51 return false;
52 if (LHS.valueless_by_exception())
53 return true;
54 // We want to dispatch to DenseMapInfo<T>::isEqual(LHS.get(I), RHS.get(I))
55 // We know the types are the same, but std::visit(V, LHS, RHS) doesn't.
56 // We erase the type held in LHS to void*, and dispatch over RHS.
57 const void *ErasedLHS =
58 std::visit([](const auto &LHS) -> const void * { return &LHS; }, LHS);
59 return std::visit(
60 [&](const auto &RHS) -> bool {
61 using T = std::remove_cv_t<std::remove_reference_t<decltype(RHS)>>;
62 return DenseMapInfo<T>::isEqual(*static_cast<const T *>(ErasedLHS),
63 RHS);
64 },
65 RHS);
66 }
67};
68
69} // end namespace llvm
70
71#endif // LLVM_ADT_DENSEMAPINFOVARIANT_H
72

source code of llvm/include/llvm/ADT/DenseMapInfoVariant.h