I have a (hopefully) simple question:
I have some classes:
class Foo
class Foo1 : Foo
class Foo2 : Foo
I have two dictionaries:
Dictionary<int, Foo1> dic1
Dictionary<int, Foo2> dic2
And I have a method:
private static int Method(Dictionary<int, Foo>)
and a method call:
Method(dic1);
but now I get the error that I can't convert Dictionary<int, Foo1> to Dictionary<int, Foo>.
How do I solve this problem?
Thank you :)
Generics, with a constraint of Foo should do it
public class Foo { }
public class Foo1 : Foo { }
public class Foo2 : Foo { }
public class SomeClass
{
public static int Method<T>(Dictionary<int, T> dict) where T : Foo
{
...
}
}
Additional Resources
Constraints on type parameters (C# Programming Guide)
Constraints inform the compiler about the capabilities a type argument must have. Without any constraints, the type argument could be any type. The compiler can only assume the members of Object, which is the ultimate base class for any .NET type.
...
By constraining the type parameter, you increase the number of allowable operations and method calls to those supported by the constraining type and all types in its inheritance hierarchy. When you design generic classes or methods, if you will be performing any operation on the generic members beyond simple assignment or calling any methods not supported by System.Object, you will have to apply constraints to the type parameter.
...
For example, the base class constraint tells the compiler that only objects of this type or derived from this type will be used as type arguments. Once the compiler has this guarantee, it can allow methods of that type to be called in the generic class.
Aside from limiting the type of the Dictionary, there are two features to support this: Covariance and Contravariance.
They allow you to treat a collection of a more/less derived type, like one of another type. So a Foo1[] could be assigned to a Foo[], same way you would assign a Foo1 to a Foo variable.
Here is the whole offocial article on the mater: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/