Jon Skeet 的 Singleton 澄清 [英] Singleton by Jon Skeet clarification

问题描述

public sealed class Singleton
{
    Singleton() {}

    public static Singleton Instance
    {
        get
        {
            return Nested.instance;
        }
    }

    class Nested
    {
        // Explicit static constructor to tell C# compiler
        // not to mark type as beforefieldinit
        static Nested() {}
        internal static readonly Singleton instance = new Singleton();
    }
}

我希望在我当前的 C# 应用程序中实现Jon Skeet 的单例模式.

I wish to implement Jon Skeet's Singleton pattern in my current application in C#.

我对代码有两个疑问

1. 如何访问嵌套类内部的外部类?我是说

1. How is it possible to access the outer class inside nested class? I mean

internal static readonly Singleton instance = new Singleton();

什么叫做闭包?

我无法理解此评论

// Explicit static constructor to tell C# compiler
// not to mark type as beforefieldinit

这条评论对我们有什么启示?

what does this comment suggest us?

推荐答案

1. 不，这与闭包无关.嵌套类可以访问其外部类的私有成员，包括此处的私有构造函数.

1. No, this is nothing to do with closures. A nested class has access to its outer class's private members, including the private constructor here.

阅读我关于 beforefieldinit 的文章.您可能需要也可能不需要 no-op 静态构造函数 - 这取决于您需要什么惰性保证.您应该知道 .NET 4 稍微改变了实际类型初始化语义(仍在规范范围内，但比以前更懒惰).

Read my article on beforefieldinit. You may or may not want the no-op static constructor - it depends on what laziness guarantees you need. You should be aware that .NET 4 changes the actual type initialization semantics somewhat (still within the spec, but lazier than before).

你真的需要这种模式吗?你确定你不能逃脱:

Do you really need this pattern though? Are you sure you can't get away with:

public sealed class Singleton
{
    private static readonly Singleton instance = new Singleton();
    public static Singleton Instance { get { return instance; } }

    static Singleton() {}
    private Singleton() {}
}

这篇关于Jon Skeet 的 Singleton 澄清的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！