slot-value

(slot-value object 'slot-name)

Reads a slot of a defclass instance, and is also a setf-able place. The slot name must be a literal quoted symbol; it resolves to the slot's fixed position at compile/expansion time, so a computed slot name is an error, and a slot name used at different positions by two unrelated classes is rejected as ambiguous (within one inheritance chain positions always agree — prefer :accessor/:reader functions, which are per-class). Reading does not type-check the object, like defstruct accessors.