The documentation for the FileManager function attributesOfItem(atPath:) says the following:

"As a convenience, NSDictionary provides a set of methods (declared as a category on NSDictionary) for quickly and efficiently obtaining attribute information from the returned dictionary: fileGroupOwnerAccountName(), fileModificationDate(), fileOwnerAccountName(), filePosixPermissions(), fileSize(), fileSystemFileNumber(), fileSystemNumber(), and fileType()."

But trying to use these convenience methods (which I thought would be "extension" but Apple is calling them "category") does not work.

let fm2 = FileManager.default
let lPath = "/Users/Guest"
do {
    let aOI1 = try fm2.attributesOfItem(atPath: lPath)
    // aOI1 is a dictionary
    if let fS = aOI1[FileAttributeKey.size] {
        print("FileSize ",fS)
    }
    // The following does not compile
    //
    // Error: Value of type '[FileAttributeKey:Any]' has no member 'fileSize'
    //let fS2 = aOI1.fileSize()
    if let pP = aOI1[FileAttributeKey.posixPermissions] {
        print("posix ",pP)
    }
    // The following does not compile
    // Error: "This method is defined on NSDictionary, and may not
    // be available in this context"
    //let pP2 = aOI1.filePosixPermission()
} catch {
    print("Error")
}

I'm using XCode 13.3 with Swift 5.6.

Obviously I'm missing something here. The Apple documentation for attributesOfItem(atPath: lPath) specifically notes the convenience methods defined on NSDictionary but although they exist I can't seem to call them successfully. Perhaps it is better to just use the FileAttributeKey.??? but I wonder how the Apple supplied "category methods" work.