Using the `is` operator with Generics in C#

Question

I want to do something like this:

class SomeClass<T>
{
   SomeClass()
   {
        bool IsInterface = T is ISomeInterface;
   }
}

What is the best way for something like this?

Note: I am not looking to constrain T with a where, but I would like my code to be aware of what types of interfaces T implements. I would prefer that I don't have to construct a T.

If you're checking types in a generic method/class, IMO something is wrong. — spender
– spender, Commented Feb 19, 2010 at 20:13
I don't want to have 3 separate descendants of SomeClass. I want some class to certain things depending if T has something. — Daniel A. White
– Daniel A. White, Commented Feb 19, 2010 at 20:18

Fredrik Mörk · Accepted Answer · 2010-02-19 20:12:55Z

33

I don't think you can use the is operator for this. But you can use IsAssignableFrom:

bool IsInterface = typeof(ISomeInterface).IsAssignableFrom(typeof(T));

answered Feb 19, 2010 at 20:12

Fredrik Mörk

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jv42 · Accepted Answer · 2018-04-24 13:58:29Z

9

should use following instead

 bool IsInterface = typeof(ISomeInterface).IsAssignableFrom(typeof(T));

is operator

is operator is used to check whether the run-time type of an object is compatible with a given type.

An expression where the use of is conforms to the syntax, evaluates to true, if both of the following conditions are met:

expression is not null.
expression can be cast to type. That is, a cast expression of the form (type)(expression) will complete without throwing an exception. For more information, see 7.6.6 Cast expressions.

References

edited Apr 24, 2018 at 13:58

jv42

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answered Feb 19, 2010 at 20:13

Asad

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Comments

SwDevMan81 · Accepted Answer · 2010-02-19 20:14:19Z

1

You can use IsAssignableFrom:

  class SomeClass<T>
  {
     SomeClass()
     {
        bool IsIComparable = typeof(IComparable).IsAssignableFrom(typeof(T));
     }
  }

answered Feb 19, 2010 at 20:14

SwDevMan81

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Patrick Desjardins · Accepted Answer · 2010-02-19 20:14:30Z

1

bool IsInterface = typeof(ISomeInterface).IsAssignableFrom(typeof(T))

answered Feb 19, 2010 at 20:14

Patrick Desjardins

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James Curran · Accepted Answer · 2010-02-19 20:13:12Z

0

I believe the best you can do it:

bool IsInterface = typeof(ISomeInterface).IsAssignableFrom(typeof(T));

answered Feb 19, 2010 at 20:13

James Curran

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GWLlosa · Accepted Answer · 2010-02-19 20:14:14Z

0

You could try doing something like

Type Ttype = typeof(T);

That will give you the full power of the Type class, which has functions like "FindInterfaces".

answered Feb 19, 2010 at 20:14

GWLlosa

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