C# extend indexer?

Question

Is it possible to use extension methods to extend an indexer? I want to be able to get cell's value from DataGridViewCell of given DataGridViewRow using header text like this:

    object o = row["HeaderText"]; 

I have this code

    public static class Ext
    {
        public static object Cells(this DataGridViewRow r, string header)
        {
            foreach (DataGridViewCell c in r.Cells)
            {
                if (c.OwningColumn.HeaderText == header)
                {
                    return c.Value;
                }
            }
            return null;
        }
    }

and I want similar indexer. Thanks.

Answer 1

Indexers are actually properties, and extension properties do not exist in C#. So this can't be done the way you want.

See this blog post for some background on the subject, and an explanation as to why that feature was considered, but ultimately omitted from C# 3.0.

Answer 2

No, it isn't. Extension methods are just syntactic sugar for static method call, an indexer is a property.

Doing

object o = new object();
o.ExtensionMethod();

is equivalent to

object o = new object();
Extensions.ExtensionMethod(o);

Extension methods don't change the class in any way, they just provide you with a simpler interface to call static methods.

Answer 3

Unfortunately, no. This would effectively be an "extension property", which isn't supported. You must have it as a method, like your current code.

Note that extension properties have been requested on Connect on multiple occasions, but have never been included in the language.

Answer 4

No you cant extend operators, such as the indexer, with extension methods.

Answer 5

No this is not possible. Extension methods are limited to methods only. They can't provide properties, indexers or constructors

Answer 6

As a workaround for an extension property you can implement Getter and Setter Extension methods for object using reflection based object indexer code.