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Diffstat (limited to 'include/ftl/expected.h')
| -rw-r--r-- | include/ftl/expected.h | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/include/ftl/expected.h b/include/ftl/expected.h index 57448dc1e0..7e765c5681 100644 --- a/include/ftl/expected.h +++ b/include/ftl/expected.h @@ -69,6 +69,36 @@ exp_.value(); \ }) +// Given an expression `expr` that evaluates to an ftl::Expected<T, E> result (R for short), +// FTL_EXPECT unwraps T out of R, or bails out of the enclosing function F if R has an error E. +// While FTL_TRY bails out with R, FTL_EXPECT bails out with E, which is useful when F does not +// need to propagate R because T is not relevant to the caller. +// +// Example usage: +// +// using StringExp = ftl::Expected<std::string, std::errc>; +// +// std::errc repeat(StringExp exp, std::string& out) { +// const std::string str = FTL_EXPECT(exp); +// out = str + str; +// return std::errc::operation_in_progress; +// } +// +// std::string str; +// assert(std::errc::operation_in_progress == repeat(StringExp("ha"s), str)); +// assert("haha"s == str); +// assert(std::errc::bad_message == repeat(ftl::Unexpected(std::errc::bad_message), str)); +// assert("haha"s == str); +// +#define FTL_EXPECT(expr) \ + ({ \ + auto exp_ = (expr); \ + if (!exp_.has_value()) { \ + return std::move(exp_.error()); \ + } \ + exp_.value(); \ + }) + namespace android::ftl { // Superset of base::expected<T, E> with monadic operations. |