suppose you have an object ? (defclass foo () ((test :accessor test :initform #'equal :initarg :test))) ==> #<STANDARD-CLASS FOO> ? (setf *foo* (make-instance 'foo :test #'eql)) ? (test *foo*) => #'eql Now you want to make another instance of foo that has the test as foo. ? (setf *new-foo* (make-instance (type-of foo))) ? (test *new-foo*) => #'equal Wait, we wanted *new-foo* to have slot test to be #'eql. This seems trival for simple objects, but consider this from make-filtered-graph (make-graph (type-of old-graph) :vertex-test (vertex-test old-graph) :vertex-key (vertex-key old-graph) :edge-test (edge-test old-graph) :edge-key (edge-key old-graph) :default-edge-type (default-edge-type old-graph) :default-edge-class (default-edge-class old-graph) :directed-edge-class (directed-edge-class old-graph) :undirected-edge-class (undirected-edge-class old-graph)))) Yuck! So we offer copy-template as a reasonable, though not perfect, solution.
| copy-template < STANDARD-OBJECT > |