Base subclass of NSTextStorage in Swift

NSTextStorageSubclass.swift

import Cocoa

@objc
class SomeTextStorage: NSTextStorage {
    
    private var storage: NSMutableAttributedString
    
    override init() {
        storage = NSMutableAttributedString(string: "", attributes: nil)
        super.init()
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("\(__FUNCTION__) is not supported")
    }
    
    required init?(pasteboardPropertyList propertyList: AnyObject, ofType type: String) {
        fatalError("\(__FUNCTION__) is not supported")
    }
    
    // MARK: NSTextStorage Primitive Methods
    // https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/TextStorageLayer/Tasks/Subclassing.html
    
    override var string: String {
        return storage.string
    }
    
    override func attributesAtIndex(location: Int, effectiveRange range: NSRangePointer) -> [String : AnyObject] {
        return storage.attributesAtIndex(location, effectiveRange: range)
    }
    
    override func replaceCharactersInRange(range: NSRange, withString str: String) {
        beginEditing()
        storage.replaceCharactersInRange(range, withString: str)
        edited(.EditedCharacters, range: range, changeInLength: (str as NSString).length - range.length)
        endEditing()
    }
    
    override func setAttributes(attrs: [String : AnyObject]?, range: NSRange) {
        beginEditing()
        storage.setAttributes(attrs, range: range)
        edited(.EditedAttributes, range: range, changeInLength: 0)
        endEditing()
    }

}