What's the function of a static constructor in a non static class?

Question

I've noticed that a non-static class can have a static constructor:

public class Thing
{
    public Thing()
    {
        Console.WriteLine("non-static");
    }

    static Thing()
    {
        Console.WriteLine("static");
    }
}

And when you initialize an instance of Thing the static constructor gets called first.

Output:

static

non-static

What would be the need for this? Do you use it to initialize static fields on your instance of the non-static type?

Are there any things to take into consideration when using a static constructor?

Solution 1

Do you use it to initialize static fields on your instance of the non-static type?

Pretty much, except that static fields (or static members of any kind) aren't associated with instances; they are associated with the type itself, regardless of whether it is a static class or a non-static class.

The documentation lists some properties of static constructors, one of which is:

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

Here, "before" means "immediately before", and whichever one of those things happens first. This is because a static constructor is only called once per type in a single program execution.

---

Are there any things to take into consideration when using a static constructor?

Here's the full list as given by the link above, which should give you an idea of what to expect when using a static constructor:

• A static constructor does not take access modifiers or have parameters.

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

• A static constructor cannot be called directly.

• The user has no control on when the static constructor is executed in the program.

• A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.

• Static constructors are also useful when creating wrapper classes for unmanaged code, when the constructor can call the LoadLibrary method.

• If a static constructor throws an exception, the runtime will not invoke it a second time, and the type will remain uninitialized for the lifetime of the application domain in which your program is running.

Besides making sure you don't try to access non-static members, since you're not in an instance constructor, the other main thing you have to consider is that a static constructor is always called at a specific time during program execution. As stated, you cannot control this, other than by controlling when "the first instance is created or any static members are referenced."

Solution 2

From MSDN Link:

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

As you stated it is used to initialize static fields. You only need to consider one thing, non-static fields are not initialized until you create instance of class.

Solution 3

You use it to initialize or invoke static members of your class.

Solution 4

• Static Constructor is called automatically before first instance of the class is created.
• Declared by prefixing a static keyword to the constructor definition.
• It can not not take access modifiers or have any parameters.

Solution 5

This is a subjective answer from personal experience, but you can also use it to ensure the initialization of other static variables outside your class, which members of your class may depend on.

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