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Bug 1637599 - Simplify propagation of error results. r=froydnj

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Differential Revision: https://phabricator.services.mozilla.com/D75090
This commit is contained in:
Simon Giesecke 2020-05-13 15:44:31 +00:00
parent 92345feaaa
commit 4a309d690e
1 changed files with 29 additions and 15 deletions
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44
mfbt/Result.h
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@ -406,6 +406,21 @@ class MOZ_MUST_USE_TYPE Result final {
return mImpl.inspectErr(); return mImpl.inspectErr();
} }
/** Propagate the error value from this Result, which must be an error result.
*
* This can be used to propagate an error from a function call to the caller
* with a different value type, but the same error type:
*
* Result<T1, E> Func1() {
* Result<T2, E> res = Func2();
* if (res.isErr()) { return res.propagateErr(); }
* }
*/
GenericErrorResult<E> propagateErr() {
MOZ_ASSERT(isErr());
return GenericErrorResult<E>{mImpl.unwrapErr()};
}
/** /**
* Map a function V -> W over this result's success variant. If this result is * Map a function V -> W over this result's success variant. If this result is
* an error, do not invoke the function and return a copy of the error. * an error, do not invoke the function and return a copy of the error.
@ -499,8 +514,7 @@ class MOZ_MUST_USE_TYPE Result final {
template <typename F, typename = std::enable_if_t<detail::IsResult< template <typename F, typename = std::enable_if_t<detail::IsResult<
decltype((*((F*)nullptr))(*((V*)nullptr)))>::value>> decltype((*((F*)nullptr))(*((V*)nullptr)))>::value>>
auto andThen(F f) -> decltype(f(*((V*)nullptr))) { auto andThen(F f) -> decltype(f(*((V*)nullptr))) {
return MOZ_LIKELY(isOk()) ? f(unwrap()) return MOZ_LIKELY(isOk()) ? f(unwrap()) : propagateErr();
: GenericErrorResult<E>(unwrapErr());
} }
}; };
@ -535,12 +549,12 @@ inline GenericErrorResult<E> Err(E&& aErrorValue) {
* discards the result altogether. On error, it immediately returns an error * discards the result altogether. On error, it immediately returns an error
* Result from the enclosing function. * Result from the enclosing function.
*/ */
#define MOZ_TRY(expr) \ #define MOZ_TRY(expr) \
do { \ do { \
auto mozTryTempResult_ = ::mozilla::ToResult(expr); \ auto mozTryTempResult_ = ::mozilla::ToResult(expr); \
if (MOZ_UNLIKELY(mozTryTempResult_.isErr())) { \ if (MOZ_UNLIKELY(mozTryTempResult_.isErr())) { \
return ::mozilla::Err(mozTryTempResult_.unwrapErr()); \ return mozTryTempResult_.propagateErr(); \
} \ } \
} while (0) } while (0)
/** /**
@ -550,13 +564,13 @@ inline GenericErrorResult<E> Err(E&& aErrorValue) {
* immediately returns the error result. |target| must evaluate to a reference * immediately returns the error result. |target| must evaluate to a reference
* without any side effects. * without any side effects.
*/ */
#define MOZ_TRY_VAR(target, expr) \ #define MOZ_TRY_VAR(target, expr) \
do { \ do { \
auto mozTryVarTempResult_ = (expr); \ auto mozTryVarTempResult_ = (expr); \
if (MOZ_UNLIKELY(mozTryVarTempResult_.isErr())) { \ if (MOZ_UNLIKELY(mozTryVarTempResult_.isErr())) { \
return ::mozilla::Err(mozTryVarTempResult_.unwrapErr()); \ return mozTryVarTempResult_.propagateErr(); \
} \ } \
(target) = mozTryVarTempResult_.unwrap(); \ (target) = mozTryVarTempResult_.unwrap(); \
} while (0) } while (0)
#endif // mozilla_Result_h #endif // mozilla_Result_h