How to make IEnumerable readonly?

Question

Why are the lists list1Instance and p in the Main method of the below code pointing to the same collection?

class Person
         


        

Answer 1

If your person object is a real object then you should consider using an immutable version.

 public class Person
 {
     public FirstName {get; private set;}
     public LastName {get; private set;}
     public Person(firstName, lastName)
     {
         FirstName = firstName;
         LastName = lastName;
     }
  }

In this way its not possible to change the content of the instance once created and therefore it isn't important that existing instances are reused in multiple lists.

Answer 2

Return a new instance of Person that is a copy of p instead of p itself in Get(). You'll need a method to make a deep-copy of a Person object to do this. This won't make them read only, but they will be different than those in the original list.

public IEnumerable<Person> Get()
{
    foreach (Person p in l1)
    {
        yield return p.Clone();
    }
}