Static constructor [SOLVED]

[mabrahao]

I am learning C# and OOP, i just cant understand how a static constructor can be useful... can someone please help me with this?? if possible, can u give a simple example? thank you very much... Marcus Abrahão Thank you all very much for your help

modified on Wednesday, January 6, 2010 7:12 AM

[Saksida Bojan]

mabrahao wrote:

static constructor can be useful

No such thing. static is usefull if you call function without intilizing class. If you intilize, constructor is called

public class Test
{
// Constructor
public Test(){}

public static Color GetColor()
{
return Color.White;
}
}

// somewher in your app

Color c = Test.GetColor(); // Test t = New Test() was never called.

[V 0]

Have a look on MSDN[^] Hope this helps.

V.
Stop smoking so you can: Enjoy longer the money you save. Moviereview Archive

[OriginalGriff]

Saksida Bojan wrote:

mabrahao wrote: static constructor can be useful No such thing. static is usefull if you call function without intilizing class. If you intilize, constructor is called

This turns out not to be the case: Static Constructor[^]

All those who believe in psycho kinesis, raise my hand.

[mabrahao]

Ok, static methods and static class was able to figure out how it works, but not the STATIC CONSTRUCTOR, like so: public class Test { int numTest; // Static Constructor static Test() { numTest = 5; } } i am reading a book from Andrew Troelsen, about C#, and in the book, he gives a example of a static constructor, but i just could not understand... anyway, thank u for u help Marcus Abrahão

[Saksida Bojan]

Thats good to know. I didn't even think it was possible

[OriginalGriff]

If you have a static class, or there is init for the class which must be done once per application (rather than done once for each instance of the class) then use a static constructor. See here: Static Constructor[^]

All those who believe in psycho kinesis, raise my hand.

[mabrahao]

Thank you, this was helpful Marcus Abrahão

[mabrahao]

Thank you Marcus Abrahão

[Pete OHanlon]

Saksida Bojan wrote:

No such thing.

What are you talking about? Of course there is. You might find reviewing this[^] useful.

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[Saksida Bojan]

I didn't know it was even possible.

[dojohansen]

I wouldn't use the terminology "static constructor" (as ALL constructors are NECESSARILY static - you cannot invoke an instance method until you've constructed an intance). But there certainly is something that (in C#) uses the keyword "static" followed by same syntax as a constructor - the class initializer. Class initializers can be used if you want to perform initialization of some kind once before a type can be used. For example, let's say you are making a bookmaker system. The prices (odds) may vary from 1.01 to 1000, but not everything in between is legal. Instead you have something like this:

From To Increment
1.01 2.00 0.01
2.02 4.00 0.02
4.04 10.00 0.05
....
500 1000 10

You could use an Int32 to store the integral number of 1/100 units, i.e. 125 for 1.25, and cover more than the range you need. But if there are only 256 legal prices you could store it in just a byte. This could make a big difference when tens of thousands of transactions per hour are to be handled, especially in terms of writing data to a database. Anyway, it doesn't really matter for our purposes whether or not the representation is useful! The point is this is a good candidate for a type initializer. Given a byte value of 135, we need to find price number 135 of the legal prices. So we can equip the class with an array and initialize the type before it's used like this:

public class OddsPrice
{
// --- Class members --- //

// Legal prices in ascending order.
static int[] priceArray;

// Type initializer: Initializes price array.
static OddsPrice()
{
priceArray = new int[256];
int price = 100; // cents
int i = 0;
while ((price += 1) <= 200) priceArray[i++] = price;
while ((price += 2) <= 400) priceArray[i++] = price;
...
}

// --- Instance members --- //

// Byte representation of value: Index in ordered set of legal values.
byte value;

// Value in cents
public int Value
{
get { return priceArray[value]; }
}
}

The type initializer will be called automatically at an undefined time (in current implementations of the CLR I believe it happens when the assembly is loaded, but the spec says undefined so don't assume anything) prior to the type being used at run-time. The advantage is that you do not need to handle any thread-syncing to ensure it runs once and only once and before anything else on the type can be used.