bkietz commented on code in PR #46792:
URL: https://github.com/apache/arrow/pull/46792#discussion_r2150698929
##########
cpp/src/arrow/status.h:
##########
@@ -350,6 +343,30 @@ class ARROW_EXPORT [[nodiscard]] Status : public
util::EqualityComparable<Status
return FromArgs(code(), std::forward<Args>(args)...).WithDetail(detail());
}
+ /// \brief Apply a functor if the status indicates an error
+ ///
+ /// If the status indicates a success, it is returned as-is.
+ ///
+ /// If the status indicates an error, the given functor is called with the
status
+ /// as argument.
+ /// If the functor returns a new Status, it is returned.
+ /// If the functor returns a Status-compatible object such as Result<T>, it
is
+ /// converted to Status and returned.
+ /// If the functor returns void, the original Status is returned.
+ template <typename OnError>
+ Status OrElse(OnError&& on_error) {
+ using RT = decltype(on_error(Status(StatusCode::UnknownError, "")));
Review Comment:
```suggestion
using RT = decltype(on_error(Status()));
```
Since this is unevaluated, we don't need to force an error status
##########
cpp/src/arrow/status.h:
##########
@@ -463,13 +480,16 @@ Status& Status::operator&=(Status&& s) noexcept {
}
/// \endcond
-namespace internal {
-
-// Extract Status from Status or Result<T>
-// Useful for the status check macros such as RETURN_NOT_OK.
-inline const Status& GenericToStatus(const Status& st) { return st; }
-inline Status GenericToStatus(Status&& st) { return std::move(st); }
+constexpr inline const Status& ToArrowStatus(const Status& st) { return st; }
Review Comment:
What you're proposing here is essentially a trait; in order to extend
`my_namespace::Err` with convertibility to status, we implement
`my_namespace::ToArrowStatus`. This extensibility sounds quite useful, but it
might be more robust and easier to explain if it were provided as a
user-specializable template struct as with many other traits:
```c++
namespace arrow::internal {
template <typename T>
struct IntoStatus;
}
namespace arrow {
/// The actual entry point
template <typename T>
constexpr decltype(auto) ToStatus(T&& t) {
return IntoStatus<T>::ToStatus(std::forward<T>(t));
}
}
namespace arrow::internal {
template <>
struct IntoStatus<Status> {
static constexpr Status& ToStatus(const Status& st) { return st; }
static constexpr Status&& ToStatus(Status&& st) { return st; }
};
template <typename T>
struct IntoStatus<Result<T>> {
static constexpr Status& ToStatus(const Result<T>& r) { return r.status();
}
static constexpr Status&& ToStatus(Result<T>&& st) { return
std::move(r).status(); }
};
} // namespace arrow
// ...
namespace arrow::internal {
template <>
struct IntoStatus<my_namespace::StatusLike> {
static Status ToStatus(my_namespace::StatusLike v) {
if (v.value == 42) {
return Status::OK();
} else {
return Status::UnknownError("StatusLike: ", v.value);
}
}
};
} // namespace arrow::internal
```
##########
cpp/src/arrow/status.h:
##########
@@ -350,6 +343,30 @@ class ARROW_EXPORT [[nodiscard]] Status : public
util::EqualityComparable<Status
return FromArgs(code(), std::forward<Args>(args)...).WithDetail(detail());
}
+ /// \brief Apply a functor if the status indicates an error
+ ///
+ /// If the status indicates a success, it is returned as-is.
+ ///
+ /// If the status indicates an error, the given functor is called with the
status
+ /// as argument.
+ /// If the functor returns a new Status, it is returned.
+ /// If the functor returns a Status-compatible object such as Result<T>, it
is
+ /// converted to Status and returned.
+ /// If the functor returns void, the original Status is returned.
+ template <typename OnError>
+ Status OrElse(OnError&& on_error) {
+ using RT = decltype(on_error(Status(StatusCode::UnknownError, "")));
+ if (ARROW_PREDICT_TRUE(ok())) {
+ return *this;
+ }
+ if constexpr (std::is_same_v<RT, void>) {
Review Comment:
```suggestion
if constexpr (std::is_void_v<RT>) {
```
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