How to use indexers with Extension Methods having out parameter and function calls

Question

Is it possible to use indexers with extension methods.

eg. Consider it as an example only.

    public static object SelectedValue(this DataGridView dgv, string ColumnName)
    {            
        return dgv.SelectedRows[0].Cells[ColumnName].Value;
    }

EDIT

1. usage mygrid.SelectedValue("mycol")

2. How to use it as an indexer mygrid.SelectedValue["mycol"] rather than above one.

3. Is it possible to use it like this as well ? mygrid.SelectedValue["mycol"](out somevalue);

What are the syntax of getting this kind of values. Any simple example or link will work.

Answer 1

Well, there are two issues here:

• C# doesn't (by and large) support named indexers¹
• C# doesn't support extension properties, so you can't make SelectedValue a property returning something indexable instead

So no, the syntax you've specified there won't work. You could get this to work:

mygrid.SelectedValue()["mycol"]

but that's a bit ugly. I'd stick with the method form if I were you.

---

¹ C# 4 supports calling named indexers on COM objects.

Answer 2

Let me try to clarify the usage and intentions of Extension Method.

Consider a Extension Method

public static string IsNullOrEmpty(this string source)
{
    return source == null || source == string.Empty;
}

Now you extend your string class with this Extension Method

var myString = "Hello World";
Assert.AreEqual(myString.IsNullOrEmpty(), false);

This is what .NET does on compilation:

public string IsNullOrEmpty(string source)
{
    return source == null || source == string.Empty;
}

Using our old school

var myString = "Hello World";
Assert.AreEqual(IsNullOrEmpty(myString), false);

Extension method is nothing but a visualization to what we were used to do.

Well, extending indexers could be possible but Microsoft did not think about it.