Hello. I am having some trouble figuring out what is going on in this Android sample Specifically

sealed class Result<out R>

From the generics documentation

The general rule is: when a type parameter 

T

 of a class 

C

 is declared out, it may occur only in out-position in the members of 

C

, but in return 

C<Base>

 can safely be a supertype of 

C<Derived>

.

In “clever words” they say that the class 

C

 is covariant in the parameter 

T

, or that 

T

 is a covariant type parameter. You can think of C as being a producer of `T`'s, and NOT a consumer of `T`’s.

So I can see that type parameter

R

of class

Result

can only be returned by

Result

,

Error

and

toString

but what is

R

? Is my assumption correct? I can see here that it is a callable reference

References to functions, properties, and constructors, apart from introspecting the program structure, can also be called or used as instances of function types.

The common supertype for all callable references is 

KCallable<out R>

, where 

R

 is the return value type, which is the property type for properties, and the constructed type for constructors.

But I am not sure what that is or why it matters here. Is this applicable to this sealed class or is this not considered a callable reference since it is a sealed class? Is the constructor the callable reference and then the return type is

Change<R>

?

ViewState 🙂

Can you clarify what you mean? Thanks!