CS0311 no implicit reference conversion between two inheriting generics

[PlayCreatively]

gameObject.AddComponent<Renderer>();

I'm getting this error for the line above

Error	CS0311	The type 'Renderer' cannot be used as type parameter 'T' in the generic type or method 'Extensions.AddComponent<T>(IGameObject)'. There is no implicit reference conversion from 'Renderer' to 'IComponent<IGameObject>'.

This is the extension method AddComponent that I'm invoking

public static T AddComponent<T>(this IGameObject gameObject) where T : IComponent<IGameObject>, new()

This is the Renderer class which inherits Component<GameObject>...

public sealed class Renderer : Component<GameObject>, IHasExtents

...which inherits IComponent<T> where T : IGameObject

public abstract class Component<T> : GameComponent, IComponent<T> where T : IGameObject

As you can see, Renderer should inherit IComponent<IGameObject>, so why do I get an error that there is no implicit reference conversion from 'Renderer' to 'IComponent<IGameObject>'?

[HaloFour]

It's a question of variance. Component<GameObject> is a subtype of IComponent<GameObject>, but IComponent<GameObject> is not a subtype of IComponent<IGameObject>.

[PlayCreatively]

Ah, thank you very much! Changing IComponent<GameObject> to IComponent<IGameObject> did the trick.
But I do find that to be peculiar since GameObject implements IGameObject, so I would have thought it would be equivalent 🤔

[Richiban]

Changing IComponent<T> to IComponent<out T> should accomplish what you want; you'll be more limited in what members you can put in the interface though.