     
     public func createBlock(data: O) -> UID {
         
-        var pos = registerBlock()
+        let pos = registerBlock()
         
         writeBlock(data, atPos: pos)
         

    
    func deleteBlock(aID: UID) -> CUnsignedLongLong {
        
        var pos = self.seekToFileID(aID)
        
        var block = Block(used: false)
        
        writeBlock(block)
        

        // update fileOffset
        
        let firstChar = "X"
        let data : NSData! = firstChar.dataUsingEncoding(NSUTF8StringEncoding)
        
        // TRUE if the operation succeeds, otherwise FALSE.
        // TODO ERROR HANDLING
        do {
            try data.writeToURL(self.url, options: NSDataWritingOptions.DataWritingAtomic)
        } catch {
            return false
        }
        
        return true
    }
    
    // subclasses should overide this method
