I have a program that defines a class
namespace #default
{
public class Test
{
}
}
I then referance another library that has no namespaces with a class called Test. How can I hide this other libraries Test class so that my program does not see #default.Test as the other libraries Test class?
By default, inside your default namespace, the default.Test class is the one that will be used when you say Test.
Outside your default namespace, you will need to do something like this in your using statements:
using ExternalTest = global::Test;
using Test = default.Test;
The first line isn't strictly necessary, as you could use global::Test anywhere.
For those that haven't encountered global before: global (C# Reference).
Prefix the identifier name with global:: to indicate that it should be found starting at the global (unnamed) namespace. For example:
class Test { }
namespace Default {
public class Test {
global::Test theOtherOne;
}
}
You'll often see it used in auto-generated code to avoid accidental name collisions. Like Resources.Designer.cs
Related
I'm finding some frustration with the way C# handles namespaces when I want to reference a class whose class name happens to be identical to part of the current class's namespace. This will produce a compiler error, "'Class' is a namespace but is used like a type".
Consider the following code sample, which demonstrates the problem:
namespace A.B.C
{
public class Y
{
}
}
namespace X.Y.Z
{
public class Class1
{
public Y MyProp;
}
}
In this case, I want to use the class "Y" from the namespace "A.B.C". But because "Y" is also one of the parts of the namespace, C# treats "Y" as a namespace, not a type.
I can get around this by fully qualifying the class name, "A.B.C.Y", or using an alias, but my general preference would be for C# not to treat "Y" as a namespace in this context. Often I have code, such as test code, that contains similar namespaces as classes its testing, and this kind of class/namespace collision means having to be a lot more verbose in setting things up.
I'm not sure what the process is called, but it seems that in resolving classes and namespaces, C# will walk up the namespaces until it finds a part of the namespace that matches. In this case, it walks up and finds Y. Is there a way to tell C# not to walk up, not to allow this partial namespace matching?
If you write using A.B.C; (the namespace that Y is in) inside namespace X.Y.Z, the error goes away:
namespace X.Y.Z
{
using A.B.C;
public class Class1
{
public Y MyProp;
}
}
I'm a student learning mainly C++, but this term we have to code our math assignments using C#.
Our professor supplied a basic skeleton program but I'm not very good at C#. He gave us two class files (.cs) but when I add them to my project, I'm unable to utilize them at all. I can't create a class object from either class.
The classes are just Line3d and Point3d. They have the variables needed to compute points and collision.
Thanks for any advice.
Compile your project.
Use Ctrl + . or bulb icon (type your class name you want to use and locate your cursor position over that class name) to resolve namespace for these classes or write using directive manually.
C# classes are normally encapsulated in namespaces. In Visual Studio, adding a new class will generate a file containing a namespace similar to PROJECT_NAME.SUBFOLDER.SUBSUBFOLDER For example:
// MyClass.cs
using System;
namespace MyProject
{
public class MyClass
{
}
}
And then you can reference that from another class in the same namespace, but you can't reference it from a class in another namespace (unless it's a namespace that starts with MyProject.).
// Line3d.cs
using System;
namespace TemplateProject
{
public class Line3d
{
}
}
// MyClass.cs
using System;
namespace MyProject
{
public class MyClass
{
public Line3d LineInstance {get;set;}
}
}
In this example, it won't work because the compiler doesn't know which namespace Line3d exists in (and, indeed, two class with the exact same name could exist in two different namespaces). You need to instruct the compiler to include classes from the TemplateProject namespace (note this doesn't include classes in the TemplateProject.ChildNamespace namespace):
// MyClass.cs
using System;
using TemplateProject;
namespace MyProject
{
public class MyClass
{
public Line3d LineInstance {get;set;}
}
}
Now you should be able to find the Line3d class and use it.
Besides manually referencing the namespace, you can also right-click an unknown class reference, select "Quick actions and Refactorings...", and then you will see something like "using TemplateProject;". Click on this and it will automatically add the using for you.
You can also use the Ctrl+. keyboard shortcut, which does the same as right-click/Quick actions, if you don't want to use the mouse.
select your project and press [ Shift + Alt + A ] to add existing files.
you can see dialog form that allows to open cs file on project.
After that, you can use professor's class files.
I was wondering Why I can access class when I defined it outside of namespace scope?
I am not very familiar with namespaces, I am just learning, but I thought that namespace should like wrap all my classes to one 'box' and they can access each other just inside that 'box' (scope).
Code example:
class Point
{
public int X;
}
namespace ConsoleApplication12
{
class Program
{
static void Main(string[] args)
{
Point p = new Point();
p.X = 50;
Console.WriteLine(p.X);
Console.ReadLine();
}
}
}
Thank you for answers.
Namespaces have nothing to do with access. It's important to differentiate between namespaces and assemblies - they're often closely related, in that types in a namespace Foo.Bar would be likely to be in assembly Foo.Bar.dll, but that's a convention - it's not something the compiler or language cares about.
A namespace is primarily "a space in which names have to be unique". In other words, while it's fine to have two types called Point in different namespaces, you can't have two types called Point in the same namespace. Indeed, the primary reason for namespaces existing (IMO) is so that we don't all have to use completely unique names across every piece of .NET code in the world.
You can use your Point class which is implicitly internal so long as it's declared within the same assembly. If it's in the global namespace (i.e. not declared in a namespace at all) then you don't need any using directives to refer to it - the purpose of a using directive is to allow you to refer to members of a different namespace just by their short name.
So if you have:
namespace Foo.Bar
{
public class Baz {}
}
then you could access that as either:
namespace Other
{
class Test
{
Foo.Bar.Baz baz = new Foo.Bar.Baz();
}
}
or
// Allow anything in namespace Foo.Bar to be accessed by its
// short name
using Foo.Bar;
namespace Other
{
class Test
{
Baz baz = new Baz();
}
}
If the type is defined in the "global" namespace, then you just don't need the using directive. From the C# 5 language specification section 3.8 (namespace and type names) where it's describing the type name lookup procedure:
If the previous steps were unsuccessful then, for each namespace N, starting with the namespace in which the namespace-or-type-name occurs, continuing with each enclosing namespace (if any), and ending with the global namespace, the following steps are evaluated until an entity is located
So in your case, looking for Point from your Main method, first ConsoleApplication12 would be checked for a Point type, then the global namespace.
To access class, outside namespace, your class should be public
public class Point
and in your namespace, where you want to see this class, you need to add namespace in top of usings
using mynamespace.external;
Than you can access your class
One article about namespaces says
Namespaces are C# program elements designed to help you organize your
programs. They also provide assistance in avoiding name clashes
between two sets of code. Implementing Namespaces in your own code is
a good habit because it is likely to save you from problems later when
you want to reuse some of your code. For example, if you created a
class named Console, you would need to put it in your own namespace to
ensure that there wasn't any confusion about when the System.Console
class should be used or when your class should be used.
Now imagine as in above statement I indeed created a Console class inside my namespace called: myNamespace.
Now at some point when someone wants to use say my library, he/she will have to do:
using myNamespace;
but likely she will need to do
using System;
too.
So we still have a clash. If I type Console, which console am I referring to?
How is this problem solved using namespaces?
PS. extra: also how namespaces work under the hood: I remember somewhere I read compiler just prepends functions for example with namespace to find their definitions?
Is this that? Is namespace really nothing just a means to group code?
If you use both of the namespaces, you will either have to fully qualify the usages(System.Console()), or use namespace/type aliases(Console2) to disambiguate the types.
using Console1 = myNamespace;
using Console2 = System;
public void MyMethod()
{
Console1.Console(); // or myNamespace.Console()
Console2.Console(); // or System.Console()
}
You would not include both using statements.
You choose, so your code looks cleaner:
using System;
public static void Main()
{
Console.WriteLine("I'm here!");
myNameSpace.Console.PopBeer("Mo beer!");
}
for practical purposes, if you have a really long namespace, you can use aliases too:
using System;
using sexyNs = myProject.AwesomeSolution.Helpers;
public static void Main()
{
Console.WriteLine("I'm here!");
sexyNs.Console.PopBeer("Mo beer!");
}
The program will not compile. You need to instantiate your classes like this:
System.Console.WriteLine("hi");
myNamespace.Console y = .... ;
a better solution would be to avoid using names which cause conflicts. Name your Console something else so it's clear which one you use when you need to.
#user200300,already many have given exact code solution to your problem description.But let me try to explain clearly.Namespaces also provide assistance in avoiding names clashes.
For example:Lets say there is a single project called Stackoverflow and it contains two teams say TeamA and TeamB.
namespace Stackoverflow
{
namespace TeamA
{
class classA
{
public static void Print()
{
Console.WriteLine("Print A");
}
}
}
}
namespace Stackoverflow
{
namespace TeamB
{
class classA
{
public static void Print()
{
Console.WriteLine("Print B");
}
}
}
}
Here both the team TeamA and TeamB are trying to modify same class classA.Namespaces have helped in organizing the code in efficient and in proper accessible way.
If you want to access the print method from any team you outside these namespaces or from any class for that matter you would write like
Stackoverflow.TeamA.classA.Print();
Stackoverflow.TeamB.classA.Print();
So above code is cumbersome and lengthy and its not clean.Hence aliases can be used .
using STAP=Stackoverflow.TeamA;
using STBP=Stackoverflow.TeamB();
Now you can access easily.
STAP.classA.print();//TeamA's print method.
Thus a namespace can contain Namespace,Class,Inteface,struct,enum,delegate
I am writing code for a game, and wanted to include my main method in two different namespaces so that it could easily access all the classes from both the 'Engine' and 'Core' Namespaces.
namespace Engine Core
{
class ExampleClass
{
}
}
Although I just put a space between Engine and Core, I know that this syntax is incorrect, I would like to know how to make a class a member of multiple namespaces. If this is not possible, is there anything that I could do that would act the same? (Classes in neither these two namespaces having to refer to this class by 'Engine.' or 'Core.'
A class can not belong to two different namespaces.
If you want to refer to a class of the Engine or Core namespaces without explicitly writing the namespace each time you reference a type of those namespaces, just use using at the beginning of the file. The using directive allows the use of types in a namespace so that you do not have to qualify the use of a type in that namespace:
using Engine;
or
using Core;
Check the documentation: using Directive
So you want someone to be able to access ExampleClass by using Engine.ExampleClass and Core.ExampleClass? I'm not sure why you would (I'm sure you have your reasons) but two ways to expose something like this are:
namespace Foo
{
abstract class ExampleClass
{
//Only implement the class here
}
}
namespace Engine
{
class ExampleClass : Foo.ExampleClass
{
//Don't implement anything here (other than constructors to call base constructors)
}
}
namespace Core
{
class ExampleClass : Foo.ExampleClass
{
//Don't implement anything here (other than constructors to call base constructors)
}
}
Or you could use namespace aliasing but every cs file using the class would require the alias to be defined.
using Engine = Core;