Swift Language Error Handling Catching different error types
Example
Let's create our own error type for this example.
2.2
enum CustomError: ErrorType {
case SomeError
case AnotherError
}
func throwing() throws {
throw CustomError.SomeError
}
3.0
enum CustomError: Error {
case someError
case anotherError
}
func throwing() throws {
throw CustomError.someError
}
The Do-Catch syntax allows to catch a thrown error, and automatically creates a constant named error available in the catch block:
do {
try throwing()
} catch {
print(error)
}
You can also declare a variable yourself:
do {
try throwing()
} catch let oops {
print(oops)
}
It's also possible to chain different catch statements. This is convenient if several types of errors can be thrown in the Do block.
Here the Do-Catch will first attempt to cast the error as a CustomError, then as an NSError if the custom type was not matched.
2.2
do {
try somethingMayThrow()
} catch let custom as CustomError {
print(custom)
} catch let error as NSError {
print(error)
}
3.0
In Swift 3, no need to explicitly downcast to NSError.
do {
try somethingMayThrow()
} catch let custom as CustomError {
print(custom)
} catch {
print(error)
}
