mfbt/ResultExtensions.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   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
   8  * results. */
   9
  10 #ifndef mozilla_ResultExtensions_h
  11 #define mozilla_ResultExtensions_h
  12
  13 #include "mozilla/Assertions.h"
  14 #include "nscore.h"
  15 #include "prtypes.h"
  16
  17 namespace mozilla {
  18
  19 // Allow nsresult errors to automatically convert to nsresult values, so MOZ_TRY
  20 // can be used in XPCOM methods with Result<T, nserror> results.
  21 template <>
  22 class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult> {
  23   nsresult mErrorValue;
  24
  25   template <typename V, typename E2>
  26   friend class Result;
  27
  28  public:
  29   explicit GenericErrorResult(nsresult aErrorValue) : mErrorValue(aErrorValue) {
  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> ToResult(nsresult aValue) {
  46   if (NS_FAILED(aValue)) {
  47     return Err(aValue);
  48   }
  49   return Ok();
  50 }
  51
  52 inline Result<Ok, nsresult> ToResult(PRStatus aValue) {
  53   if (aValue == PR_SUCCESS) {
  54     return Ok();
  55   }
  56   return Err(NS_ERROR_FAILURE);
  57 }
  58
  59 }  // namespace mozilla
  60
  61 #endif  // mozilla_ResultExtensions_h