Extending a property and in meanwhile insert a new item

Question

This is my code:

var myList = myPage.News.Cast<MyNew>();

MyNew have somethings like 20 property (Name, Title, Date, Place, etc etc) but it miss one, the property (for example) Tel.

Can't recreate my whole structure (it also become from a DLL), so I'd like to faster add a property of MyNew called Tel, inside that list. So extend the class during the insert in a list.

You could add it as an extension method called `Tel()` to `MyNew` perhaps? No extension properties sadly. — Lloyd, Mar 06 '13 at 14:44
Is the `MyNew` class sealed as if it is not you might be able to inherit from the class adding on any properties you need — Kane, Mar 06 '13 at 14:44
Are you expecting that this property should be available on compile time so you can fere to it in a C# code or it participates in run time stuff only? — sll, Mar 06 '13 at 14:44

score 3 · Answer 1 · answered Mar 06 '13 at 14:45

No, but you could create an anonymous type that includes the original type plus your new column:

var myList = myPage.News
                   .Cast<MyNew>()
                   .Select( new { m => MyNew = m,
                                       Tel = [formula for tel]
                                }
                          );

Jeffrey Knight · Answer 2 · 2013-03-06T15:09:41.097

1

public class MyNewExtended: MyNew {
   public String Tel { get;set; }
}

var myList = myPage.News.Cast<MyNewExtended>();

(but see Chris Sinclair's comment below)

edited Mar 06 '13 at 15:09

answered Mar 06 '13 at 14:46

Jeffrey Knight

5,888
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2

Assuming `News` is `IEnumerable`, the `Cast` will fail because they _aren't actually_ objects of the subclass type. – Chris Sinclair Mar 06 '13 at 14:47
I had no idea Cast() was so tricky ("the behaviour of Cast() was changed between .NET 3.5 and .NET 3.5 SP1") -- http://stackoverflow.com/questions/445471/puzzling-enumerable-cast-invalidcastexception – Jeffrey Knight Mar 06 '13 at 15:01
1

Just think of it like a literal type-cast to a _subclass_. It will _not_ perform any _conversion_ even if an explicit/implicit conversion exists. (but since `MyNewExtended` extends `MyNew` you wouldn't be able to write a user-defined conversion anyway) – Chris Sinclair Mar 06 '13 at 15:16

score -1 · Answer 3 · answered Mar 06 '13 at 14:47

-1

You should be able to extend MyNew with a partial class like so:

public partial class MyNew
{
    public int Tel { get; set; }
}

Tel will then be available like any other property.

answered Mar 06 '13 at 14:47

Vaze

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Can't use `partial` because the class is already compiled in another DLL. – Chris Sinclair Mar 06 '13 at 14:48
2

Partial is just a way of splitting a class across files. The class has to be partial in the first place. – Ben Robinson Mar 06 '13 at 14:49
-1 Vaze re-read how the OP is explaining his issue in his question. `partial class won't help` – MethodMan Mar 06 '13 at 14:49
Sorry. You're right. I didn't see that it was from another DLL. – Vaze Mar 06 '13 at 14:53

Extending a property and in meanwhile insert a new item

3 Answers3