Convert List Type to IEnumerable Interface Type

Question

I have a

List<Person> personlist; 

How can I convert to

IEnumerable<IPerson> iPersonList

Person Implements IPerson interface

Answer 1

If you're in .NET 4.0 or later, you can just do an implicit cast:

IEnumerable<IPerson> iPersonList = personlist;
//or explicit:
var iPersonList = (IEnumerable<IPerson>)personlist;

This uses generic contravariance in IEnumerable<out T> - i.e. since you only ever get something out of an IEnumerable, you can implicitly convert IEnumerable<T> to IEnumerable<U> if T : U. (It also uses that List<T> : IEnumerable<T>.)

Otherwise, you have to cast each item using LINQ:

var iPersonList = personlist.Cast<IPerson>();