mfbt/ResultExtensions.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
   2  * vim: set ts=8 sts=4 et sw=4 tw=99:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /* Extensions to the Result type to enable simpler handling of XPCOM/NSPR results. */
   8
   9 #ifndef mozilla_ResultExtensions_h
  10 #define mozilla_ResultExtensions_h
  11
  12 #include "mozilla/Assertions.h"
  13 #include "nscore.h"
  14 #include "prtypes.h"
  15
  16 namespace mozilla {
  17
  18 // Allow nsresult errors to automatically convert to nsresult values, so MOZ_TRY
  19 // can be used in XPCOM methods with Result<T, nserror> results.
  20 template <>
  21 class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult>
  22 {
  23   nsresult mErrorValue;
  24
  25   template<typename V, typename E2> friend class Result;
  26
  27 public:
  28   explicit GenericErrorResult(nsresult aErrorValue) : mErrorValue(aErrorValue)
  29   {
  30     MOZ_ASSERT(NS_FAILED(aErrorValue));
  31   }
  32
  33   operator nsresult() { return mErrorValue; }
  34 };
  35
  36 // Allow MOZ_TRY to handle `PRStatus` values.
  37 inline Result<Ok, nsresult> ToResult(PRStatus aValue);
  38
  39 } // namespace mozilla
  40
  41 #include "mozilla/Result.h"
  42
  43 namespace mozilla {
  44
  45 inline Result<Ok, nsresult>
  46 ToResult(nsresult aValue)
  47 {
  48   if (NS_FAILED(aValue)) {
  49     return Err(aValue);
  50   }
  51   return Ok();
  52 }
  53
  54 inline Result<Ok, nsresult>
  55 ToResult(PRStatus aValue)
  56 {
  57   if (aValue == PR_SUCCESS) {
  58     return Ok();
  59   }
  60   return Err(NS_ERROR_FAILURE);
  61 }
  62
  63 } // namespace mozilla
  64
  65 #endif // mozilla_ResultExtensions_h