How get the list of errors thrown by a function?

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When the Swift docs says a function throws, they mean that it throws an ErrorType (in Cocoa APIs usually an NSError), not an exception.

Consider the following do-try-catch flow for NSFileManager‘s createDirectoryAtPath:

let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0]

do {
    try NSFileManager.defaultManager().createDirectoryAtPath(documentsPath, withIntermediateDirectories: false, attributes: nil)
} catch { 
    // 'error' variable automatically populated
    print(error)
    print(error.dynamicType)
}

createDirectoryAtPath will fail because the documents directory already exists. Logging the dynamicType of the error shows that it is in fact an NSError object:

Error Domain=NSCocoaErrorDomain Code=516 "The file “Documents” couldn’t be saved in the folder “35B0B3BF-D502-4BA0-A991-D07568AB87C6” because a file with the same name already exists." UserInfo={NSFilePath=/Users/jal/Library/Developer/CoreSimulator/Devices/E8A35774-C9B7-42F0-93F1-8103FBBC7118/data/Containers/Data/Application/35B0B3BF-D502-4BA0-A991-D07568AB87C6/Documents, NSUnderlyingError=0x7fa88bd14410 {Error Domain=NSPOSIXErrorDomain Code=17 "File exists"}}

NSError

In order to see the different types of errors a function can throw, you would have to examine the error for information to determine the type of error thrown, and how to handle each error. In the case of NSError this would be its domain, code, and description.

In this particular case, a directory already exists at that path, so the file manager cannot create a new directory. An example of another reason why this operation could fail would be if the file manager did not have write access. That would be error code 256.

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