在C＃中初始化靜態變量內聯或靜態構造函數的差異

Question

我想知道初始化內聯靜態成員有什么區別，如：

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

或者在靜態構造函數中初始化它，如：

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

Answer 1

如果類型中有靜態構造函數，則由於不再應用beforefieldinit標志而導致類型初始化。

它還影響初始化順序 - 變量初始化程序都在靜態構造函數之前執行。

據我所知，這就是它。

Answer 2

在這種情況下，我不相信有任何實際差異。 如果在初始化靜態變量時需要一些邏輯 - 比如如果你想在給定不同條件的情況下使用不同的接口具體類型 - 那么你將使用靜態構造函數。 另外，內聯初始化在我的書中很好。

class Foo
{
    private static IBar _bar;

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

Answer 3

Twilight zone回答：內聯初始化器和ctor分配之間的執行順序有所不同......當你混合實例和靜態成員和繼承來引導時。

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.

示例:)

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();

輸出：

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