c# - Passing method with list of base type in return type as a parameter causes wrong method signature error -

i'm trying create generic method filter results several method returning lists of types deriving same base type. prepared simplified version of problem:

using system; using system.collections.generic; using system.linq;  public class animal  {     public string name { get; set; } } public class cat : animal { } public class dog : animal { }   public class program {     public static void main()     {         console.writeline(getfilteredanimals("pe", getcats));     }      private static list<cat> getcats()     {            return new list<cat>() { new cat { name = "sphinx" }, new cat { name = "persian" } };     }      private static list<dog> getdogs()     {         return new list<dog>() { new dog { name = "bulldog"}, new dog { name = "dalmatian" } };     }      private static list<animal> getfilteredanimals(string f, func<list<animal>> method)     {         var animals = method();           return animals.where(a => a.name.startswith(f)).tolist<animal>();     } } 

the method

getfilteredanimals("pe", getcats) 

does not work because getcats not return list of animal. possible such generic method lists? far know, if used single objects instead of lists work.

the working code here on .net fiddle

assuming you're using c# 4+ , .net 4+, can work using generic covariance:

private static list<animal> getfilteredanimals(string f, func<ienumerable<animal>> method) 

a list<cat> can't treated list<animal> - can treated ienumerable<animal> because ienumerable<t> covariant in t.

likewise func<t> covariant in t, func<list<cat>> can treated func<ienumerable<animal>>... compiles.