c# - 在 C# 中内联或在静态构造函数中初始化静态变量的区别

Question

我想知道初始化静态成员内联有什么区别：

class Foo
{
    private static Bar bar_ = new Bar();
}

或在静态构造函数中初始化它，如下所示：

class Foo
{
    static Foo()
    {
        bar_ = new Bar();
    }
    private static Bar bar_;
}

Answer 1

如果您的类型中有静态构造函数，它会更改类型初始化，因为不再应用beforefieldinit标志。

它还影响初始化顺序 - 变量初始化器都在静态构造函数之前执行。

据我所知，这就是它。

Answer 2

在这种情况下，我认为没有任何实际区别。如果您在初始化静态变量时需要一些逻辑 - 例如，如果您想在给定不同条件的情况下使用不同的具体接口类型 - 您将使用静态构造函数。否则，内联初始化在我的书中很好。

class Foo
{
    private static IBar _bar;

    static Foo()
    {
        if(something)
        {
            _bar = new BarA();
        }
        else
        {
            _bar = new BarB();
        }
    }
}

Answer 3

暮光之城答案：内联初始化程序和 ctor 分配之间的执行顺序有所不同......当您混合实例和静态成员以及继承启动时。

For static members, static initializers 
Static ctors (execute bottom up)
Base static initializer
Base static ctor and so on

For instance members, initializers in current class execute first
Then initializers in base class execute ( up the chain)
Then top-most base ctor is executed (and we walk down now. Instance ctors execute top-down)
Finally current type's ctor is executed.

例子 ：）

public class CBase
    {
        static Talkative m_Baseob1 = new Talkative("Base Static Initializer-");
        static Talkative m_Baseob2;
        Talkative m_Baseob3 = new Talkative("Base Inst Initializer");
        Talkative m_Baseob4;
        static CBase()
        {
            Console.WriteLine("***MethodBegin: Static Base Ctor");
            m_Baseob2 = new Talkative("Base Static Ctor");
            Console.WriteLine("***MethodEnd: Static Base Ctor");
        }
        public CBase()
        {
            Console.WriteLine("***MethodBegin: Instance Base Ctor");
            m_Baseob4 = new Talkative("Base Instance Ctor");
            Console.WriteLine("***MethodEnd: Instance Base Ctor");
        }
    }
    public class CDerived : CBase
    {
        static Talkative m_ob1 = new Talkative("Derived Static Initializer");
        static Talkative m_ob2;
        Talkative m_ob3 = new Talkative("Derived Inst Initializer");
        Talkative m_ob4;
        static CDerived()
        {
            Console.WriteLine("***MethodBegin: Derived Static Ctor");
            m_ob2 = new Talkative("Derived Static Ctor");
            Console.WriteLine("***MethodEnd: Derived Static Ctor");
        }
        public CDerived()
        {
            Console.WriteLine("***MethodBegin: Derived Instance Ctor");
            m_ob4 = new Talkative("Derived Instance Ctor");
            Console.WriteLine("***MethodEnd: Derived Instance Ctor");
        }
    }
    internal class Talkative
    {
        public Talkative(string sID)
        {
            Console.WriteLine(sID + " - Talkative created" );
        }
    }

    # Main function somewhere
    CDerived s = new CDerived();

输出：

Derived Static Initializer - Talkative created

***MethodBegin: Derived Static Ctor
Derived Static Ctor - Talkative created
***MethodEnd: Derived Static Ctor

Derived Inst Initializer - Talkative created

Base Static Initializer- - Talkative created

***MethodBegin: Static Base Ctor
Base Static Ctor - Talkative created
***MethodEnd: Static Base Ctor

Base Inst Initializer - Talkative created

***MethodBegin: Instance Base Ctor
Base Instance Ctor - Talkative created
***MethodEnd: Instance Base Ctor

***MethodBegin: Derived Instance Ctor
Derived Instance Ctor - Talkative created
***MethodEnd: Derived Instance Ctor