How can I access functions from a class without having to name that class every time? I know how to use "using" so that I don't have to name the namespace but I was hoping there was a way to do with this static functions so that I can call them the way I would call a function in the same class.
using static yournamespace.yourclassname;
then call the static class method without class name;
Example:
Class1.cs
namespace WindowsFormsApplication1
{
class Utils
{
public static void Hello()
{
System.Diagnostics.Debug.WriteLine("Hello world!");
}
}
}
Form1.cs
using System.Windows.Forms;
using static WindowsFormsApplication1.Utils;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
Hello(); // <====== LOOK HERE
}
}
}
I routinely have
static Action<object> o = s => Console.WriteLine(s);
in my code which makes debug output so much less noisy. That way I can call Console's static Writeline() much easier. Would that help?
If you're looking to define a globally-scoped procedure then the short answer is no, you can't do this in c#. No global functions, procedures or objects.
In C# everything apart from namespaces and types (class, struct, enum, interface) must be defined inside a type. Static members (fields, properties and methods) can be used without an instance of the class, but only by referencing the type that owns them. Non-static members need an instance of the owning class.
This is fundamental to the syntax of the language. C# is neither C nor C++, where you can define global objects, functions and procedures.
In C#? Not possible. Because it's a full OOP programming language and it was designed to work with objects you can't use functions outside the scope of an object. When calling static methods you have to specify the class where that static method lives...
Class.StaticMethod();
you can only use the short-hand notation if this method is call from within the same class...
StaticMethod();
But remember that you will not get access to instance members because static methods donot belong to instance of an object
Update based on comment
Looks like it will be possible to call static members without having to specify the class that declares it in C# 6, and you will be able to reference classes directly in using statements...in similar fashion to Java...more info here
Related
i made a class in app code folder in visual studio 2010. when i declared any variable outside of a method(globally), it can't be visible in that method. I am new in asp.net, may be i make any mistake but i can't catch that. So i need some help. my code is as follow...
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
public class Class2
{
public Class2()
{
//
// TODO: Add constructor logic here
//
}
int i;
public static void calculate(string)
{
// here want that variable but i can't get it in intelliscence.
}
}
That method is static.
You cannot access an instance member from a static method. That doesn't make sense.
Think of static as "global to every possible instance of the class". Your int i variable means "global.. to a single instance of the class". When you think of it like that, it makes sense that you can't access a variable that is "global to a single instance" from a method that is "global to every instance".
Hopefully that makes sense? (probably needs to be re-phrased.. I was just trying to make it easier to understand)
A static method can only access static members.
Static methods cannot access non-static class level members. Instance methods can access static members, but must be called through an instantiated object.
A static method cannot access non static members. To use non static members, create an object of the class and then use the get/set methods.
A static method can only access static data members. You should use static variable to work in static method.
I make extensive use of member functions of one specific static class. Specifying the class name every time I call it's methods looks nasty...
Can I import a static class as a namespace to call its methods without specifying the class name C#?
The feature you were looking for was added within C# 6.0
It's called "Using Static".
Here's the link for more explanations and examples:
https://msdn.microsoft.com/en-us/magazine/dn879355.aspx
If you mean import it such that it's methods are global, no.
You might want to look at extension methods though. They are static methods that, when their class's namespace is imported, show up as instance methods on the type of their first argument. See more here: http://msdn.microsoft.com/en-us/library/bb383977.aspx
Yes, you can. C# 6 introduced new construct -
the using static directive lets you
import all the static members of a type, so that you can use those members unqualified
:
using static ClassName;
for instance:
using System;
using static System.Console;
class Program
{
static void Main()
{
WriteLine("test");
}
}
The only difference I see is the fact that you can't use the "using staticClass" declaration.
Therefore, I'm wondering:
Is there a real difference between a static class and a namespace?
Is there a possibility to avoid having to rewrite the class name every time a member function is called? I'm thinking about something analogous to "using staticClass".
Yes, a static class is technically a type. It can have members (fields, methods, events). A namespace can only hold types (and it's not considered a "type" by itself; typeof(System) is a compile-time error).
There's no direct equivalent to adding a using directive for a namespace for a static class. You can, however, declare aliases:
using ShortName = ReallyReallyLongStaticClassName;
and use
ShortName.Member
when referring its members.
Additionally, you can use static classes to declare extension methods on other types and use them directly without referring to the class name explicitly:
public static class IntExtensions {
public static int Square(this int i) { return i * i; }
}
and use it like:
int i = 2;
int iSquared = i.Square(); // note that the class name is not mentioned here.
Of course, you'll have to add a using directive for the namespace containing the class to use the extension method if the class is not declared in the root or current namespace.
Static class is still a class. It can contain methods, properties, etc. Namespace is just a namespace. It's just a helper to distinguish between class declarations with the same name.
Function can't live in a namespace alone, it belongs to a class.
Extensions is probably what you are looking for, if you need a static function without mentioning the name of the class.
public static class MathExtensions
{
public static int Square(this int x)
{
return x * x;
}
}
//...
// var hundredSquare = 100.Square();
One other difference is that namespaces can span several assemblies, while classes cannot.
As far as I understand, namespaces are a language feature only; they get removed by compilation. In other words, the .NET runtime does not "see" namespaces, just class names that happen to contain dots. For example, the String class in the System namespace is seen by the .NET runtime as a class named System.String, but there is no concept of namespace at all.
Static classes, however, are fully understood and managed by the .NET runtime. They are fully-fledged types and you can use reflection on them.
Do they have the equivalent of C# static classes in Java?
I want to create a C# static class but in Java, how do I do it?
Thanks for the help.
EDIT: Thanks for the help guys. :)
There are static members in Java classes, but no static class, like in C#.
The C# static class modifier doesn't really change anything about the class, from a usage standpoint, though. It just prevents you, at compile time, from adding instance variables.
You can make a class in Java that would work like a C# static class by just declaring every member as static. See the tutorial section on "Understanding Instance and Class Members" for details.
No. Just mark everything static. Possibly add a private constructor that throws an error and make the class final.
Try this:
public class Util
{
// final prevents inheritance, just like C# static classes can't be inherited
// final is basically like the C# sealed keyword.
public static final class Math
{
// prevent constructor from being called
private Math(){}
static
{
// Acts like a C# static constructor. (only runs once, )
}
public static int Add(int num1, int num2)
{
return num1+num2;
}
}
}
In every OO language,a good (an more flexible) alternative to static class declaration is to use the singleton pattern.
However, if your class is a pure utility class, you can declare all your members/methods as static.
I have several classes that do not really need any state. From the organizational point of view, I would like to put them into hierarchy.
But it seems I can't declare inheritance for static classes.
Something like that:
public static class Base
{
}
public static class Inherited : Base
{
}
will not work.
Why have the designers of the language closed that possibility?
Citation from here:
This is actually by design. There seems to be no good reason to inherit a static class. It has public static members that you can always access via the class name itself. The only reasons I have seen for inheriting static stuff have been bad ones, such as saving a couple of characters of typing.
There may be reason to consider mechanisms to bring static members directly into scope (and we will in fact consider this after the Orcas product cycle), but static class inheritance is not the way to go: It is the wrong mechanism to use, and works only for static members that happen to reside in a static class.
(Mads Torgersen, C# Language PM)
Other opinions from channel9
Inheritance in .NET works only on instance base. Static methods are defined on the type level not on the instance level. That is why overriding doesn't work with static methods/properties/events...
Static methods are only held once in memory. There is no virtual table etc. that is created for them.
If you invoke an instance method in .NET, you always give it the current instance. This is hidden by the .NET runtime, but it happens. Each instance method has as first argument a pointer (reference) to the object that the method is run on. This doesn't happen with static methods (as they are defined on type level). How should the compiler decide to select the method to invoke?
(littleguru)
And as a valuable idea, littleguru has a partial "workaround" for this issue: the Singleton pattern.
The main reason that you cannot inherit a static class is that they are abstract and sealed (this also prevents any instance of them from being created).
So this:
static class Foo { }
compiles to this IL:
.class private abstract auto ansi sealed beforefieldinit Foo
extends [mscorlib]System.Object
{
}
Think about it this way: you access static members via type name, like this:
MyStaticType.MyStaticMember();
Were you to inherit from that class, you would have to access it via the new type name:
MyNewType.MyStaticMember();
Thus, the new item bears no relationships to the original when used in code. There would be no way to take advantage of any inheritance relationship for things like polymorphism.
Perhaps you're thinking you just want to extend some of the items in the original class. In that case, there's nothing preventing you from just using a member of the original in an entirely new type.
Perhaps you want to add methods to an existing static type. You can do that already via extension methods.
Perhaps you want to be able to pass a static Type to a function at runtime and call a method on that type, without knowing exactly what the method does. In that case, you can use an Interface.
So, in the end you don't really gain anything from inheriting static classes.
Hmmm... would it be much different if you just had non-static classes filled with static methods..?
What you want to achieve by using class hierarchy can be achieved merely through namespacing. So languages that support namespapces ( like C#) will have no use of implementing class hierarchy of static classes. Since you can not instantiate any of the classes, all you need is a hierarchical organization of class definitions which you can obtain through the use of namespaces
You can use composition instead... this will allow you to access class objects from the static type. But still cant implements interfaces or abstract classes
Although you can access "inherited" static members through the inherited classes name, static members are not really inherited. This is in part why they can't be virtual or abstract and can't be overridden. In your example, if you declared a Base.Method(), the compiler will map a call to Inherited.Method() back to Base.Method() anyway. You might as well call Base.Method() explicitly. You can write a small test and see the result with Reflector.
So... if you can't inherit static members, and if static classes can contain only static members, what good would inheriting a static class do?
A workaround you can do is not use static classes but hide the constructor so the classes static members are the only thing accessible outside the class. The result is an inheritable "static" class essentially:
public class TestClass<T>
{
protected TestClass()
{ }
public static T Add(T x, T y)
{
return (dynamic)x + (dynamic)y;
}
}
public class TestClass : TestClass<double>
{
// Inherited classes will also need to have protected constructors to prevent people from creating instances of them.
protected TestClass()
{ }
}
TestClass.Add(3.0, 4.0)
TestClass<int>.Add(3, 4)
// Creating a class instance is not allowed because the constructors are inaccessible.
// new TestClass();
// new TestClass<int>();
Unfortunately because of the "by-design" language limitation we can't do:
public static class TestClass<T>
{
public static T Add(T x, T y)
{
return (dynamic)x + (dynamic)y;
}
}
public static class TestClass : TestClass<double>
{
}
You can do something that will look like static inheritance.
Here is the trick:
public abstract class StaticBase<TSuccessor>
where TSuccessor : StaticBase<TSuccessor>, new()
{
protected static readonly TSuccessor Instance = new TSuccessor();
}
Then you can do this:
public class Base : StaticBase<Base>
{
public Base()
{
}
public void MethodA()
{
}
}
public class Inherited : Base
{
private Inherited()
{
}
public new static void MethodA()
{
Instance.MethodA();
}
}
The Inherited class is not static itself, but we don't allow to create it. It actually has inherited static constructor which builds Base, and all properties and methods of Base available as static. Now the only thing left to do make static wrappers for each method and property you need to expose to your static context.
There are downsides like the need for manual creation of static wrapper methods and new keyword. But this approach helps support something that is really similar to static inheritance.
P.S.
We used this for creating compiled queries, and this actually can be replaced with ConcurrentDictionary, but a static read-only field with its thread safety was good enough.
My answer: poor design choice. ;-)
This is an interesting debate focused on syntax impact. The core of the argument, in my view, is that a design decision led to sealed static classes. A focus on transparency of the static class's names appearing at the top level instead of hiding ('confusing') behind child names? One can image a language implementation that could access the base or the child directly, confusing.
A pseudo example, assuming static inheritance was defined in some way.
public static class MyStaticBase
{
SomeType AttributeBase;
}
public static class MyStaticChild : MyStaticBase
{
SomeType AttributeChild;
}
would lead to:
// ...
DoSomethingTo(MyStaticBase.AttributeBase);
// ...
which could (would?) impact the same storage as
// ...
DoSomethingTo(MyStaticChild.AttributeBase);
// ...
Very confusing!
But wait! How would the compiler deal with MyStaticBase and MyStaticChild having the same signature defined in both? If the child overrides than my above example would NOT change the same storage, maybe? This leads to even more confusion.
I believe there is a strong informational space justification for limited static inheritance. More on the limits shortly. This pseudocode shows the value:
public static class MyStaticBase<T>
{
public static T Payload;
public static void Load(StorageSpecs);
public static void Save(StorageSpecs);
public static SomeType AttributeBase
public static SomeType MethodBase(){/*...*/};
}
Then you get:
public static class MyStaticChild : MyStaticBase<MyChildPlayloadType>
{
public static SomeType AttributeChild;
public static SomeType SomeChildMethod(){/*...*/};
// No need to create the PlayLoad, Load(), and Save().
// You, 'should' be prevented from creating them, more on this in a sec...
}
Usage looks like:
// ...
MyStaticChild.Load(FileNamePath);
MyStaticChild.Save(FileNamePath);
doSomeThing(MyStaticChild.Payload.Attribute);
doSomething(MyStaticChild.AttributeBase);
doSomeThing(MyStaticChild.AttributeChild);
// ...
The person creating the static child does not need to think about the serialization process as long as they understand any limitations that might be placed on the platform's or environment's serialization engine.
Statics (singletons and other forms of 'globals') often come up around configuration storage. Static inheritance would allow this sort of responsibility allocation to be cleanly represented in the syntax to match a hierarchy of configurations. Though, as I showed, there is plenty of potential for massive ambiguity if basic static inheritance concepts are implemented.
I believe the right design choice would be to allow static inheritance with specific limitations:
No override of anything. The child cannot replace the base
attributes, fields, or methods,... Overloading should be ok, as
long as there is a difference in signature allowing the compiler to
sort out child vs base.
Only allow generic static bases, you cannot inherit from a
non-generic static base.
You could still change the same store via a generic reference MyStaticBase<ChildPayload>.SomeBaseField. But you would be discouraged since the generic type would have to be specified. While the child reference would be cleaner: MyStaticChild.SomeBaseField.
I am not a compiler writer so I am not sure if I am missing something about the difficulties of implementing these limitations in a compiler. That said, I am a strong believer that there is an informational space need for limited static inheritance and the basic answer is that you can't because of a poor (or over simple) design choice.
Static classes and class members are used to create data and functions that can be accessed without creating an instance of the class. Static class members can be used to separate data and behavior that is independent of any object identity: the data and functions do not change regardless of what happens to the object. Static classes can be used when there is no data or behavior in the class that depends on object identity.
A class can be declared static, which indicates that it contains only static members. It is not possible to use the new keyword to create instances of a static class. Static classes are loaded automatically by the .NET Framework common language runtime (CLR) when the program or namespace that contains the class is loaded.
Use a static class to contain methods that are not associated with a particular object. For example, it is a common requirement to create a set of methods that do not act on instance data and are not associated to a specific object in your code. You could use a static class to hold those methods.
Following are the main features of a static class:
They only contain static members.
They cannot be instantiated.
They are sealed.
They cannot contain Instance Constructors (C# Programming Guide).
Creating a static class is therefore basically the same as creating a class that contains only static members and a private constructor. A private constructor prevents the class from being instantiated.
The advantage of using a static class is that the compiler can check to make sure that no instance members are accidentally added. The compiler will guarantee that instances of this class cannot be created.
Static classes are sealed and therefore cannot be inherited. They cannot inherit from any class except Object. Static classes cannot contain an instance constructor; however, they can have a static constructor. For more information, see Static Constructors (C# Programming Guide).
When we create a static class that contains only the static members and a private constructor.The only reason is that the static constructor prevent the class from being instantiated for that we can not inherit a static class .The only way to access the member of the static class by using the class name itself.Try to inherit a static class is not a good idea.
I run into the problem when trying to code an IComparer<T> implementation against a third-party library where T is an enum embedded in a class as in the following:
public class TheClass
{
public enum EnumOfInterest
{
}
}
But because the enum is defined within a third-party library class, I can't write the comparer because the following gives a "cannot extends list" error:
public class MyComparer : IComparer<TheClass.EnumOfInterest>
{
}
I'm not even extending a static class -- I'm just implementing a comparer of a enum defined in a class.