This is unrelated to the NS_REFINED_FOR_SWIFT macro. The Objective-C
method
- (BOOL) verifyPersonalizationWithError:(NSError **) error;
is imported to Swift as
open func verifyPersonalization() throws
and the only effect of the NS_REFINED_FOR_SWIFT macro is to prepend
underscores to the Swift method name
open func __verifyPersonalization() throws
which allows to provide a refined Swift interface in an extension, while keeping the original implementation available to be called from the refined interface
(see "Refining Objective-C Declarations" in Swift and Objective-C in the Same Project).
The Swift importer assumes that the boolean return value of the Objective-C method indicates success or
failure, which is the common Cocoa pattern
as documented in Using and Creating Error Objects:
Important: Success or failure is indicated by the return value of the method.
Although Cocoa methods that indirectly return error objects in the Cocoa error
domain are guaranteed to return such objects if the method indicates failure
by directly returning nil or NO, you should always check that the return
value is nil or NO before attempting to do anything with the NSError object.
A typical usage in Objective-C is
NSError *error;
if ([self verifyPersonalizationWithError:&error]) {
NSLog(@"success");
} else {
NSLog(@"failed: %@", error.localizedDescription);
}
The Swift method throws an error on failure, so there is no need
for a boolean return value:
do {
try verifyPersonalization()
print("success")
} catch {
print("failed:", error.localizedDescription)
}
If the Objective-C method really indicates failure by leaving
a non-null error in the error parameter (instead of returning false, which is the usual Cocoa pattern) then you can indicate that
by adding a attribute:
- (BOOL) verifyPersonalizationWithError:(NSError **) error
__attribute__((swift_error(nonnull_error)));
which is imported to Swift as
open func verifyPersonalization() throws -> Bool
The swift_error attribute is documented at https://github.com/apple/swift-clang/blob/383859a9c4b964af3d127b5cc8abd0a8f11dd164/include/clang/Basic/AttrDocs.td#L1800-L1819
