1//===--- MSVCErrorWorkarounds.h - Enable future<Error> in MSVC --*- 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// MSVC's promise/future implementation requires types to be default
10// constructible, so this header provides analogues of Error an Expected
11// that are default constructed in a safely destructible state.
12//
13// FIXME: Kill off this header and migrate all users to Error/Expected once we
14// move to MSVC versions that support non-default-constructible types.
15//
16//===----------------------------------------------------------------------===//
17
18#ifndef LLVM_SUPPORT_MSVCERRORWORKAROUNDS_H
19#define LLVM_SUPPORT_MSVCERRORWORKAROUNDS_H
20
21#include "llvm/Support/Error.h"
22
23namespace llvm {
24
25// A default-constructible llvm::Error that is suitable for use with MSVC's
26// std::future implementation which requires default constructible types.
27class MSVCPError : public Error {
28public:
29 MSVCPError() { (void)!!*this; }
30
31 MSVCPError(MSVCPError &&Other) : Error(std::move(Other)) {}
32
33 MSVCPError &operator=(MSVCPError Other) {
34 Error::operator=(std::move(Other));
35 return *this;
36 }
37
38 MSVCPError(Error Err) : Error(std::move(Err)) {}
39};
40
41// A default-constructible llvm::Expected that is suitable for use with MSVC's
42// std::future implementation, which requires default constructible types.
43template <typename T> class MSVCPExpected : public Expected<T> {
44public:
45 MSVCPExpected()
46 : Expected<T>(make_error<StringError>("", inconvertibleErrorCode())) {
47 consumeError(this->takeError());
48 }
49
50 MSVCPExpected(MSVCPExpected &&Other) : Expected<T>(std::move(Other)) {}
51
52 MSVCPExpected &operator=(MSVCPExpected &&Other) {
53 Expected<T>::operator=(std::move(Other));
54 return *this;
55 }
56
57 MSVCPExpected(Error Err) : Expected<T>(std::move(Err)) {}
58
59 template <typename OtherT>
60 MSVCPExpected(
61 OtherT &&Val,
62 std::enable_if_t<std::is_convertible<OtherT, T>::value> * = nullptr)
63 : Expected<T>(std::move(Val)) {}
64
65 template <class OtherT>
66 MSVCPExpected(
67 Expected<OtherT> &&Other,
68 std::enable_if_t<std::is_convertible<OtherT, T>::value> * = nullptr)
69 : Expected<T>(std::move(Other)) {}
70
71 template <class OtherT>
72 explicit MSVCPExpected(
73 Expected<OtherT> &&Other,
74 std::enable_if_t<!std::is_convertible<OtherT, T>::value> * = nullptr)
75 : Expected<T>(std::move(Other)) {}
76};
77
78} // end namespace llvm
79
80#endif // LLVM_SUPPORT_MSVCERRORWORKAROUNDS_H
81