c# - How to cast a list of concrete classes which implement an interface -

i have interface ianimal , 2 classes(dog, cat), both implement interface.

public interface ianimal {     int age { get; set; } }  public class dog : ianimal {     public int age { get; set; } }  public class cat : ianimal {     public int age { get; set; } } 

also, have animalsmanager class shown in code below.

public class animalsmanager {     private readonly list<dog> _dogs = new list<dog>();     private readonly list<cat> _cats = new list<cat>();      public void settargetanimalsage(bool isdog, int age)     {         if (isdog)         {             setanimalsage(_dogs, age);         }         else         {             setanimalsage(_cats, age);         }     }      private static void setanimalsage<t>(ienumerable<t> animals, int age) t : class, ianimal     {         foreach (var animal in animals)         {             animal.age = age;         }     } } 

in method settargetanimalsage, setanimalsage used twice depending on value of isdog argument. i'd unite these 2 usages 1, following codes not compile.

// not compile. // var animals = isdog ? _dogs : _cats; // var animals = isdog ? _dogs list<ianimal> : _cats list<ianimal>;  setanimalsage(animals, age); 

how possible handle 1 of lists of dogs , cats list of ianimal?

you can't have ilist<t> because ilist<t> not covariant ienumerable<t> covariant. can cast ienumerable<t> , should work.

for example, following code should work:

public void settargetanimalsage(bool isdog, int age) {         var animals = isdog ? (ienumerable<ianimal>)_dogs : _cats;      setanimalsage(animals, age); }