How to use the "is" keyword with an object?

Question

How can I use the is keyword with an object, rather than an object's class?

Here is some code:

private bool IsObjectCompatableWithObjects(object obj, IEnumerable<object> objects)
{
    foreach (var item in objects)
    {
        if (obj is item)
        {
            return true;
        }
    }
    return false;
}

The above code has the following error:

The type or namespace name 'item' could not be found (are you missing a using directive or an assembly reference?)

Do you want to check the types or do you want to see if the object exists in the list? — rie819, Jun 01 '16 at 11:45
Are you looking to know if object equals item or if your object is of the same type as item? — aloisdg, Jun 01 '16 at 11:47
Judging from the fuction name op is trying to check wheter an object's type fits the sequence of objects. — user6144226, Jun 01 '16 at 11:47
read about the `is` keyword [here](https://msdn.microsoft.com/en-gb/library/scekt9xw.aspx) — Ponas Justas, Jun 01 '16 at 11:48

score 0 · Answer 1 · answered Jun 01 '16 at 11:53

I guess you're trying to achieve something like this?

private bool IsObjectCompatibleWithObjects(object obj, IEnumerable<object> objects)
{
    return objects.Any(i => i.GetType().IsAssignableFrom(obj.GetType()));
}

To test:

var objects = new object[] { 7, "foo", DateTime.Now, Guid.NewGuid() };

Console.WriteLine(IsObjectCompatibleWithObjects(1, objects));
Console.WriteLine(IsObjectCompatibleWithObjects("test", objects));
Console.WriteLine(IsObjectCompatibleWithObjects(3f, objects));

Output:

True
True
False

Yogi · Answer 2 · 2016-06-01T12:25:22.063

0

is is used against the type itself and NOT against the instance of type. So if you need to check if the item is of type object probably you should write -

if (item is Object)

instead of

 if (obj is item)

But then everything is object, so it is of little help. If you need to just check if the type if item in the list is same as type object, then you should do -

 if (item.GetType() == obj.GetType())

edited Jun 01 '16 at 12:25

answered Jun 01 '16 at 11:53

Yogi

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score 0 · Answer 3 · answered Jun 01 '16 at 11:57

If you want to see if your object is include in your enumerable of objects, you can use Enumerable.Contains from System.Linq:

Determines whether a sequence contains a specified element by using the default equality comparer.

You can use it like this:

private static bool IsObjectCompatableWithObjects<T>(T obj, IEnumerable<T> objects)
{
    return objects.Contains(obj);
}

Basically, you are doing something like this:

private static bool IsObjectCompatableWithObjects<T>(T obj, IEnumerable<T> objects)
{
    foreach (var item in objects)
    {
        if (obj.Equals(item))
        {
            return true;
        }
    }
    return false;
}

You can look for the exact implementation here.

How to use the "is" keyword with an object?

3 Answers3