objc:define-objc-protocol

(objc:define-objc-protocol name &key incorporated-protocols instance-methods class-methods)

Declares the protocol name, a string, with the methods it lists as (name result-type arg-type*). It declares, it does not create: as the manual says, a protocol is not defined in Lisp, and (:objc-protocols "Name") of objc:define-objc-class adopts one the runtime already has (warning when it has none). Part of the macOS-only objc package -- the interpreter (java -jar, or the rontolisp native binary), a compiled .class / .jar and a --native executable for macOS on Apple silicon, never a .wasm. The definition needs no runtime: the Objective-C side is made when the runtime is opened (objc:ensure-objc-initialized, or the first send). See the macOS GUI guide.

MY-APP> (define-objc-protocol "NSCopying"
          :instance-methods (("copyWithZone:" objc-object-pointer (:pointer :void))))
"NSCopying"
MY-APP> (define-objc-class copyable () () (:objc-class-name "Copyable") (:objc-protocols "NSCopying"))
COPYABLE