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      typename std::enable_if<std::is_convertible<OtherT, T>::value>::type * =
63          nullptr)
64      : Expected<T>(std::move(Val)) {}
65
66  template <class OtherT>
67  MSVCPExpected(
68      Expected<OtherT> &&Other,
69      typename std::enable_if<std::is_convertible<OtherT, T>::value>::type * =
70          nullptr)
71      : Expected<T>(std::move(Other)) {}
72
73  template <class OtherT>
74  explicit MSVCPExpected(
75      Expected<OtherT> &&Other,
76      typename std::enable_if<!std::is_convertible<OtherT, T>::value>::type * =
77          nullptr)
78      : Expected<T>(std::move(Other)) {}
79};
80
81} // end namespace llvm
82
83#endif // LLVM_SUPPORT_MSVCERRORWORKAROUNDS_H
84