Types static constructor calling

Question

Possible Duplicate:
Why doesn't the CLR always call value type constructors

Found next code in Richter's book (I have simplified it a little bit):

internal struct SomeValType
{
    static SomeValType()
    {
        Console.WriteLine("This never gets displayed");
    }
    public Int32 X;
}

public sealed class Program
{
    public static void Main()
    {
        SomeValType a = new SomeValType { X = 123 };
        Console.WriteLine(a.X);
    }
}

Output:

123

Can't understand why WriteLine in static constructor nevel calls. Looked at ILDasm - constructor code and calling of method are present. If I add any static variable to SomeValType and init it in constructor then WriteLine calling correctly.

Can someone explain, please, behavior in such situation? Thanks.

I tried making X static and assigning it in the constructor. This made the console output appear as expected. Same thing happened if I removed X entirely and threw in a static method that I called in Main(). Perhaps static constructors aren't invoked unless a static method or member is called/accessed? — Martin Törnwall, May 01 '11 at 10:29

score 1 · Accepted Answer · answered May 01 '11 at 10:29

1

Probably because you're never accessing a real constructor nor a static field.

The default constructor of value types is special. It's just an initialization to binary the default value of all fields(i.e. binary zero the whole struct)

answered May 01 '11 at 10:29

CodesInChaos

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Martin Törnwall · Answer 2 · 2011-05-01T11:03:02.233

From MSDN:

A static constructor is called automatically to initialize the class [emphasis mine] before the first instance is created or any static members are referenced.

It seems that the word class is the key here. Making SomeValType a class results in a static constructor invocation upon creating the first instance of the type as stated above. When it is a struct, however, it seems you need to access a static field or call a static method for this behavior to be triggered. Is this a bug or is it intended?

Types static constructor calling

2 Answers2