objective-c - oc这段代码转化为swift 应该怎么写的？

Question

- (NSMutableArray *)orderArray {
    if (!_orderArray) {
        _orderArray = [NSMutableArray array];
    }
    return _orderArray;
}

Answer 1

If you are correct, it should be the attribute get method in Objective-C.
Actually, @Tr2e was almost completely correct. His answer could have been improved with a slight modification:

lazy var orders: [AnyObject] = []

NO:

// 如果省略 `:` 后面的类型的话，orders 的类型会变为 NSArray，
// 而不是 Swift 的类型，也不是 NSMutableArray
lazy var orders = []

(PS: orders is a better name)

Answer 2

lazy var orderArray = NSMutableArray()

Answer 3

Single case?
If hard translation

func orderArray()->NSMutableArray{
    if _orderArray != nil {
        _orderArray = NSMutableArray.array()
    }
    return _orderArray
}

Swift point

// 单例类
class SharedObject {    
    static let sharedInstance = SharedObject()
}
// 使用 
SharedObject.sharedInstance.doSomething()   

Answer 4

There is a keyword called lazy, which is roughly like this:
lazy var array = { let a = NSArray.init(); return a }()