include/llvm/Support/MSVCErrorWorkarounds.h

   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       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