如果C＃有一个懒惰的关键字，使延迟初始化更容易？

Should C# have a lazy keyword to make lazy initialization easier?

例如。

    public lazy string LazyInitializeString = GetStringFromDatabase();

而不是

推荐答案

我不知道一个关键字，但它现在有一个的 System.Lazy＆LT; T＆GT; 类型。

I don't know about a keyword but it now has a System.Lazy<T> type.

public class ClassWithLazyMember
{
    Lazy<String> lazySource;
    public String LazyValue
    {
        get
        {
            if (lazySource == null)
            {
                lazySource = new Lazy<String>(GetStringFromDatabase);
                // Same as lazySource = new Lazy<String>(() => "Hello, Lazy World!");
                // or lazySource = new Lazy<String>(() => GetStringFromDatabase());
            }
            return lazySource.Value;
        }
    }

    public String GetStringFromDatabase()
    {
        return "Hello, Lazy World!";
    }
}

测试：

var obj = new ClassWithLazyMember();

MessageBox.Show(obj.LazyValue); // Calls GetStringFromDatabase()
MessageBox.Show(obj.LazyValue); // Does not call GetStringFromDatabase()

在上面的测试code， GetStringFromDatabase（）被调用一次。我想，这正是你想要的。

In above Test code, GetStringFromDatabase() gets called only once. I think that is exactly what you want.

具有@dthorpe和@Joe的意见后，我可以说的是下面是最短的也可以是：

After having comments from @dthorpe and @Joe, all I can say is following is the shortest it can be:

public class ClassWithLazyMember
{
    Lazy<String> lazySource;
    public String LazyValue { get { return lazySource.Value; } }

    public ClassWithLazyMember()
    {
        lazySource = new Lazy<String>(GetStringFromDatabase);
    }

    public String GetStringFromDatabase()
    {
        return "Hello, Lazy World!";
    }
}

由于以下不能编译：

public Lazy<String> LazyInitializeString = new Lazy<String>(() =>
{
    return GetStringFromDatabase();
});

和该属性是的类型懒＆LT;字符串＆GT; 不是字符串。你总是需要访问它使用 LazyInitializeString.Value 的价值。

And that property is type of Lazy<String> not String. You you always need to access it's value using LazyInitializeString.Value.

和，我打开了如何把它缩短的建议。

And, I am open for suggestions on how to make it shorter.