Re: EXC_BAD_INSTRUCTION when enumerating /.DocumentRevisions-V100/
Re: EXC_BAD_INSTRUCTION when enumerating /.DocumentRevisions-V100/
- Subject: Re: EXC_BAD_INSTRUCTION when enumerating /.DocumentRevisions-V100/
- From: Jean Suisse <email@hidden>
- Date: Sat, 22 Oct 2016 21:42:40 +0200
> On 22 Oct 2016, at 21:24, Quincey Morris <email@hidden> wrote:
>
> On Oct 22, 2016, at 11:42 , Jean Suisse <email@hidden <mailto:email@hidden>> wrote:
>>
>> My app should get an access denied error (the enumerator should be nil for instance). It shouldn’t crash.
>
> It can’t return nil, because that is used to signal the end of the enumeration. I agree it’s nasty if it crashes, though.
I am not talking about enumerator?.nextObject() but about manager.enumerator(at: includingPropertiesForKeys: options:), which in the API return an optional FileManager.DirectoryEnumerator?, which I expect to be nil when there is nothing to enumerate.
However, the doc states:
Returns: An NSDirectoryEnumerator object that enumerates the contents of the directory at url. If url is a filename, the method returns an enumerator object that enumerates no files—the first call to nextObject()returns nil.
So, why make it an optional value at all?
>
>> Though it looks like I am trying to access "/.DocumentRevisions-V100/“, it is not what I am trying to achieve.
>>
>> At some point my app needs to enumerate user-selected directories. The issue is I get a crash when directories such as "/.DocumentRevisions-V100/“ are present.
>> I cannon reasonably maintain a list of “don’t enumerate” directories.
>
> It’s still not quite clear what your real code is trying to do. If you were enumerating the *root* directory *shallowly* (.skipsSubdirectoryDescendants), and you hit this directory, you should *not* try to descend explicitly into this directory (or any directory whose name begins with a period, I suppose) as your sample code does. If you were doing a deep enumeration from the root directory, you wouldn’t be executing shallow enumeration code as in your sample code.
Yes, I enumerate shallowly. Yes I hit the directory. And yes, the user may take an action that will lead my app to try enumerating directories such as "/.DocumentRevisions-V100/“ shallowly.
The finder doesn’t crash when I try to open .DocumentRevisions-V100. Neither should my app.
> Can you use the .skipsHiddenFiles option for your real enumerator? That will skip files and directories whose name starts with a period.
I could. But I still may hit directories that the user does not have the permission to access. .DocumentRevisions-V100 is really just for the example.
>
>> To refine, what difference is there between ObjC’s
>> for (NSURL* file in enumerator)
>>
>> and swift’s
>>
>> while let file = enumerator?.nextObject() as? URL
>> ?
>
> You’re comparing unlike things. Regardless of language, “for … in” and “while … nextObject” use different mechanisms for maintaining state between iterations. What does the Swift version of the “for … in” loop do?
Jens asked if an equivalent in ObjC would crash. That’s what I came up with. The for … in loop performs gathers data about the file and folders, puts them in an array, returns it to the caller function, then the app continues interacting with the user.
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