Hi All, What is the use of a static class? I mean what are benefits of using static class and how CLR deals with static classes?
+23
A:
A static class simply denotes that you don't expect or need an instance. This is useful for utility logic, where the code is not object-specific. For example, extension methods can only be written in a static class.
Pre C# 2.0, you could just have a regular class with a private constructor; but static makes it formal the you can never have an instance (there is no constructor*, and all members must be static).
(*=see comment chain; you can optionally have a type initializer (static constructor aka .cctor), but you cannot have an instance constructor (aka .ctor)).
Marc Gravell
2009-02-23 08:05:44
static class actually does have constructor.
lubos hasko
2009-02-23 08:12:01
no, it really doesn't. "static class Foo {}" compiles to IL: ".class private abstract auto ansi sealed beforefieldinit Foo extends [mscorlib]System.Object{}" - no ctor. It can *optionally* have a type initializer (.cctor), but that is different to an (instance) constructor (.ctor)
Marc Gravell
2009-02-23 08:14:38
+1 for "they really don't have constructors".
Jon Skeet
2009-02-23 08:19:07
ok, so it doesn't have contructor (you're right) but static types can have optional type initializer which in fact works like constructor. I would say your answer is still misleading if you say there is no contructor without mentioning optional type initializer.
lubos hasko
2009-02-23 08:43:39
Fine - I'll add the word "instance", but I think the comments have more than covered this.
Marc Gravell
2009-02-23 08:47:14
+2
A:
All members of a static class has to be static members, so, if you forget to add 'static' before any of them your code won't compile, it also makes your code more readable as anyone who will see that the class is static will understand it only contains static members.
The best use for a static class is for utility functions, you could also use them to keep the global methods and data in your application, I use static static classes very often in almost any project.
Waleed Eissa
2009-02-23 08:09:11
It also prevents both creating an instance (like an abstract class) and inheriting from it (like a sealed class).
configurator
2009-02-23 08:47:48
+1
A:
Static classes are sealed. This may be a useful option to use static for utility classes.
Canavar
2009-02-23 08:09:19
+2
A:
The compilation and metadata model for .net requires that all functions are defined within a class. This makes life somewhat easier and simpler for the reflection api's since the concepts of the owning class and its visibility is well defined. It also makes the il model simpler.
since this precludes free functions (ones not associated with a class) this makes the choice of where to put functions which have no associated state (and thus need for an instance). If they need no state associated with them nor have any clear instance based class to which they can be associated and thus defined within there needs to be some idiom for their definition.
Previously the best way was to define the methods within a class whose constructor was private and have none of the functions within the class construct it.
This is a little messy (since it doesn't make it crystal clear why it was done without comments) and the reflection api can still find the constructor and invoke it.
Thus static classes were allowed, making the intent of the class, that of a place for the definition of static methods, clear to users and to the type system. Static classes have no constructor at all.
ShuggyCoUk
2009-02-23 08:15:46
+2
A:
Static classes are often used to group related global services which you initially don't want to be accessed with an object instance. An example is the Math class in the .Net BCL, which you use directly, e.g., Math.Sqrt(10.0)
robi
2009-02-23 08:18:05
+2
A:
A static class is a language hack to write procedural programs in C#.
cpeterso
2009-02-26 07:14:17