let 心得

在定义一个属性，但又需要设置一些属性，可以使用下面这种形式定义。

let dateFormatter: NSDateFormatter = {
    let formatter = NSDateFormatter()
    formatter.dateFormat = "yyyy.MM.dd"
    return formatter
}()

let style: [String: NSObject] = {

    let font = UIFont(name: "HelveticaNeue-Medium", size: 16.0)!
    let textColor = UIColor.blueColor()

    let paraStyle = NSMutableParagraphStyle()
    paraStyle.lineSpacing = 5.0
    paraStyle.lineBreakMode = .ByWordWrapping
    paraStyle.paragraphSpacing = 0
    paraStyle.paragraphSpacingBefore = 0

    return [NSForegroundColorAttributeName: textColor,
        NSKernAttributeName: CGFloat(0.5),
        NSFontAttributeName: font,
        NSParagraphStyleAttributeName: paraStyle
    ]
}()

其实，我们应该尽量使用let，@NatashaTheRobot发过一条推：

Convert your CoreData NSManagedObjects into structs to avoid mutable state!

如果不需要修改属性，我觉得可以更绝决一点，

import Foundation
import CoreData

struct Task: Equatable {
    let id: String
    let title: String
}

func ==(lhs: Task, rhs: Task) -> Bool {
    return lhs.id == rhs.id && lhs.title == rhs.title
}

extension Task {
    init(managedTask: NSManagedObject) {
        id = managedTask.valueForKey("id") as! String
        title = managedTask.valueForKey("title") as! String
    }
}