Are static fields or properties initialized once?

Question

With the code below, will each call to Test.someBaseField or Test.someBaseProperty result in the function being called and a new instance of SomeBase being created? or does that only happen once at the start?

How would I set it up for the latter (called once at the start)?

public class SomeBase {}
public class SomeObjectA : SomeBase {}
public class SomeObjectB : SomeBase {}

public class Test
{
    public static bool someBool = true;

    public static SomeBase someBaseField = GetBase(someBool);
    public static SomeBase someBaseProperty { get { return GetBase(someBool); } }

    public static SomeBase GetBase(bool getA)
    {
        if(getA)
            return new SomeObjectA() as SomeBase;       
        else
            return new SomeObjectB() as SomeBase;
    }
}

Answer 1

Get base will be called each time for either property and a new instance of somebase will be returned every time. What you have going on there is called a factory.

What you are wanting to do is create a singleton. There are many methods to create singletons but the most popular is to track some field or property and return that every time if initialized or initialize it if not.

so you are looking at doing something like:

static someBase _trackingVar;
public static someBase someProperty{ 
    get
    {
        if(_trackingVar == null){
            _trackingVar = GetBase(...);
        }
        return _trackingVar;
    }
}

The one problem with this approach is that it is not thread safe. There's a thread safe version of this approach to singleton creation. See http://msdn.microsoft.com/en-us/library/ff650316.aspx for more details