CODEWITHSUNDEEP
.netgenerics
Peter PitLock
Peter PitLock

Reputation: 1873

What does "Generic Type" mean? in .net : x.GetType().IsGenericType

I have found explanations for java Generic Types, but I do understand there are major differences between Java and .net's generic Types

E.g. I run the following , but I cannot find out the true meaning of it. 

   List<int> list = new List<int>();
   Console.WriteLine( list.GetType().IsGenericType);

The MSDN link simply states "Gets a value indicating whether the current type is a generic type.", but it does not state what generic type means

Does Generic Type mean it is inherited from the Object class?

Does Generic Type have to do with Abstract classes?

What is the definition of a .net Generic Type - how can I determine whether it is a Generic Type or not, from logic by myself ( in order to understand the concept)

Upvotes: 0

Views: 558

Answers (3)

xjuice
xjuice

Reputation: 310

To answer your two questions first:

  1. All types in .NET, generic types and others derive from Object.
  2. A generic type may be abstract just like any other type but it doesn't need to be. If you make an abstract generic type you need to derive a non-abstract type from it to be able to instantiate an object from it.

To determine whether a type is generic or not, just look a the class definition. Queue is NOT a generic type, while Queue<T> is a generic type, because you can get different types by replacing the generic type parameter T with any other type. For example Queue<int>, Queue<string>, Queue<Object> etc. all use the same code defined once in Queue<T> class. Notice that they are also generic types themselves. Also nested types, which are nested in a generic type are considered to be generic types. The "base type" Queue<T> is called a generic type definition.

public abstract class MyListBase { }
public abstract class MyListBase<T> : MyListBase { }
public class MyList<T> : MyListBase<T>
{
    public class Nested { }
}
public class MyStringList : MyList<string> { }

...

var isGenericType0 = typeof(MyListBase).IsGenericType; //False
var isGenericType1 = typeof(MyListBase<>).IsGenericType; //True
var isGenericType2 = typeof(MyListBase<>)
    .MakeGenericType(typeof(char)).IsGenericType; //True
var myIntegerList = new MyList<int>();
var isGenericType3 = myIntegerList.GetType().IsGenericType; //True
var myNested1 = new MyList<int>.Nested();
var isGenericType4 = myNested1.GetType().IsGenericType; //True
var myStringList = new MyStringList();
var isGenericType5 = myStringList.GetType().IsGenericType; //False

Hope you can wrap you head around generic types now.

Upvotes: 1

Ivan
Ivan

Reputation: 312

It's hard to describe what is Generic in .NET at answer. It's better to read documentation.

In short, it's a templates in С++, Generic in Java, .NET, Delphi. Common description here

https://en.wikipedia.org/wiki/Generic_programming

Documentation from MSDN

Upvotes: 0

Ali Elmi
Ali Elmi

Reputation: 386

Generics let you tailor a method, class, structure, or interface to the precise data type it acts upon.

A generic type definition is a class, structure, or interface declaration that functions as a template, with placeholders for the types that it can contain or use. For example, the System.Collections.Generic.Dictionary class can contain two types: keys and values. Because a generic type definition is only a template, you cannot create instances of a class, structure, or interface that is a generic type definition.

public class Generic<T>
{
    public T Field;
}

Upvotes: 0

Related Questions