How to Extend the Type Class

Question

this is my code:

bool ch=Type.IsBuiltIn("System.Int32");   // not working-> syntax error


public static class MyExtentions
    {             
        public static bool IsBuiltIn(this Type t, string _type)
        {
            return (Type.GetType(_type) == null) ? false : true;
        }
    }

Please I want Extend Type Class by IsBuiltIn new method

write `typeof(int).IsBuiltIn` to your editor. What do you see? — I4V, Aug 30 '13 at 11:03
the string you pass to the IsBuiltIn() method should be assembly-qualified name of the type. I mean you should pass System.Int32 insted of just int — Dimitri, Aug 30 '13 at 11:05
"int" just isn't a built-in type. It is an *alias* that's specific to the C# compiler. Other languages use other aliases, like "Integer" in VB.NET. Given that there just a handful of aliases (don't forget the nullable ones), you can hardcode their names. Or just not do this. — Hans Passant, Aug 30 '13 at 11:14
A method such as `IsBuiltIn` doesn’t really make sense in an extensible type system. What do you need this for? Also, writing `someCondition ? false : true` makes no sense. Just write `!someCondition`. — Konrad Rudolph, Aug 30 '13 at 11:21

score 6 · Accepted Answer · answered Aug 30 '13 at 11:19

You can't have static extension methods. Your extension method works on an instance of the Type class, so to call it you'd have to do something like this:

typeof(Type).IsBuiltIn("System.Int32")

The workaround for this is to just put your extension method in a utility class, e.g. like the following, and call it like a normal static function:

public static class TypeExt
{             
    public static bool IsBuiltIn(string _type)
    {
        return Type.GetType(_type) == null;
    }
}

// To call it:
TypeExt.IsBuiltIn("System.Int32")

By the way, I don't think this will tell you whether the type is "built-in"; it will merely tell you whether a type with the given name has been loaded into the process.

score 3 · Answer 2 · answered Aug 30 '13 at 11:20

Extension methods are intended to describe new APIs on instances, not types. In your case, that API would be something like:

Type someType = typeof(string); // for example
bool isBuiltIn = someType.IsBuiltIn("Some.Other.Type");

which... clearly isn't what you wanted; the type here adds nothing and is not related to the IsBuiltIn. There is no compiler trick for adding new static methods to existing types, basically - so you will not be able to use Type.IsBuiltIn("Some.Other.Type").

score 0 · Answer 3 · edited May 23 '17 at 12:16

0

You can't extend the Type class. You need an instance of the class to create an extension method.

Edit: See here and here.

edited May 23 '17 at 12:16

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answered Aug 30 '13 at 11:03

Loetn

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Why?? why can't you do so? – Sriram Sakthivel Aug 30 '13 at 11:04
@SriramSakthivel No, you need an instance of a class type. You cannot extent the class type itself. – Maarten Aug 30 '13 at 11:07
When I downvote your answer was only this `You can't extend the Type class` Is that makes sense? – Sriram Sakthivel Aug 30 '13 at 11:08
You can of course write extension methods for `Type`. For ex `"".GetType().IsBuiltIn("")` would work (Although I don't see a good reason to do so). – I4V Aug 30 '13 at 11:09
I was editing my answer. And now you can find two links that explain it why you can't do it. – Loetn Aug 30 '13 at 11:09
@Maarten When I downvote this was the answer `You can't extend the Type class` Is that makes sense? – Sriram Sakthivel Aug 30 '13 at 11:09

How to Extend the Type Class

3 Answers3