Question

Let’s say I have instance of MyCollection class called Foo1. MyCollection is basically a collection of MyClass. Not sure how can I do something like below with or without a cast?

MyCollection Foo2 =  Foo1.Where( r => r.LastName == “SomeName”)

NOTE: MyCollection & MyClass are something from a 3rd party library. I probably can create extension method on it but hoping to have some easy way of doing it.

Answer 1

If you want to have a new instance of MyCollection holding only those elements that meet the criteria, you can create a Where method on your class.

Or, you can rely on the linq extension method on IEnumerable<T> (assuming your class implements IEnumerable<MyClass>), and use whatever method you would normally use for populating a MyCollection from a sequence of MyClass objects.

EDIT

Example of linq extension method approach:

• ensure that MyCollection implements IEnumerable<MyClass>
• ensure that MyCollection has a constructor that accepts an IEnumerable<MyClass>
• include #using System.Linq;
• example statement: MyCollection Foo2 = new MyCollection(Foo1.Where( r => r.LastName == “SomeName”));

EDIT EDIT

I see now that MyClass and MyCollection are third-party types. I had assumed from the “my” bit that you were designing them yourself.

The MyCollection type almost certainly implements IEnumerable<MyClass> — if it doesn’t, it may implement the non-generic IEnumerable. In that case, you can use the Cast<T> extension method. If it implements neither interface, the third-party library is somewhat lacking.