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 
23 namespace 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.
27 class MSVCPError : public Error {
28 public:
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.
43 template <typename T> class MSVCPExpected : public Expected<T> {
44 public:
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