fli:foreign-slot-value

(fli:foreign-slot-value pointer slot-name &key type object-type copy-foreign-object)

Answers the slot slot-name of the structure pointer points at (of type object-type when given); a list of names reaches into a nested structure. Slots are those objc:define-objc-struct declared, and cocoa:ns-rect's origin / size, cocoa:ns-point's x / y, cocoa:ns-size's width / height and cocoa:ns-range's location / length, matched by name in any package. The value is read as fli:dereference reads one, copy-foreign-object included; setf writes one. Part of the macOS-only fli package, beside objc -- 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. See the macOS GUI guide.

CL-USER> (fli:with-dynamic-foreign-objects ((rect cocoa:ns-rect))
           (objc:invoke-into rect (objc:invoke "NSValue" "valueWithRect:" #(0 0 640 480)) "rectValue")
           (fli:foreign-slot-value rect '(:size :width)))
640.0