How to do defmethod dispatch based on the type of a struct's slot?

[Okamsn <okamsn@protonmail.com>]

Hello,

I am trying to test using a `cl-defstruct` structure to represent a 
sub-sequence, which would implement `seq-map`. In the structure, I have 
a slot that contains the original sequence. I would like to be able to 
use different forms of `seq-map` based on the type of the original 
sequence. I am having trouble understanding how to create a specializer 
and a generalizer for this.

Is there a way to create a specializer for `cl-defmethod`, something 
like `(cl-defmethod seq-map (function (sequence (my-test-subseq array))) 
...)` ?

I have tried using a type defined via `cl-deftype` as the specializer 
using the `satisfies` type, but that did not seem work. Do types defined 
via `cl-deftype` work as specializers?

Thank you.