c# - 试图理解静态构造函数

Question

我正在尝试了解对静态构造函数的需求。我发现的所有信息都没有回答我提出的问题。你为什么要这样做

class SimpleClass
{
    // Static variable that must be initialized at run time.
    static readonly long baseline;

    // Static constructor is called at most one time, before any
    // instance constructor is invoked or member is accessed.
    static SimpleClass()
    {
        baseline = DateTime.Now.Ticks;
    }
}

相对于此

class SimpleClass
{
    // Static variable that must be initialized at run time.
    static readonly long baseline = DateTime.Now.Ticks;

    // Static constructor is called at most one time, before any
    // instance constructor is invoked or member is accessed.
    //static SimpleClass()
    //{

    //}
}

?

---

这不是其他问题的骗局，这是关于不接受参数的静态构造函数。

Answer 1

需求在某种程度上是显而易见的:您想要为静态成员做的不仅仅是一些字段初始化。

逻辑上如果你有这个类:

class SimpleClass
{
    // Static variable that must be initialized at run time.
    static readonly long baseline = DateTime.Now.Ticks;


}

你可以重写它来达到同样的效果:

class SimpleClass
{
    // Static variable that must be initialized at run time.
    static readonly long baseline;

    static SimpleClass () {
        baseline = DateTime.Now.Ticks;
    }   
}

但是，您可以在静态构造函数中做更多的事情，例如检查(使用反射)一些属性并向它们发出一些快速访问器/ getter ，或者只是简单地通知其他系统您的类型已创建等。

来自 Jeffrey Richter CLR via C# book:

When the C# compiler sees a class with static fields that use inline initialization (the BeforeFieldInit class), the compiler emits the class’s type definition table entry with the BeforeFieldInit metadata flag. When the C# compiler sees a class with an explicit type constructor (the Precise class), the compiler emits the class’s type definition table entry without the BeforeFieldInit metadata flag. The rationale behind this is as follows: initialization of static fields needs to be done before the fields are accessed, whereas an explicit type constructor can contain arbitrary code that can have observable side effects; this code may need to run at a precise time.

显然，幕后发生的事情远不止这些，我建议您通过 C# 阅读 CLR 的整章:“类型构造函数”