There's also a similar limitation in Kernel#class definition, where def class: () -> Class should map out to something more useful, i.e. def class: () -> instance_class, but that would require support for a new keyword, and there may be other limitations?

• Perhaps Proposal: making Class and Module classes generic -- Class[I] and Module[I] #1542?

Unfortunately, it doesn't work with the current instance type semantics.

This is an output to type check def Object.inherited(klass) = klass.fooo.

test.rb:1:36: [error] Type `::Object` does not have method `fooo`
│ Diagnostic ID: Ruby::NoMethod
│
└ def Object.inherited(klass) = klass.fooo
                                      ~~~~

The instance type is resolved to Object, not singleton(Object).

test.rb:1:36: [error] Type `::Object` does not have method `fooo`
│ Diagnostic ID: Ruby::NoMethod
│
└ def Object.inherited(klass) = klass.fooo
                                      ~~~~

The instance type is resolved to Object, not singleton(Object).

This hints that singleton(Object) only reads from Object RBS and doesn’t consider itself an instance of Class; this is an oversight.