Hi. > Am 06.02.2021 um 17:42 schrieb Pascal Bourguignon <p...@informatimago.com>: > > Le 06/02/2021 à 17:35, Pascal Bourguignon a écrit : >> Now, where would defmacro enter the scene? We could define a few macros and >> supporting functions to be able to define factories with their set of >> concrete classes; the macro would expand to the boilerplate code, such as >> the generic and methods, according to the implementation choice (alist, >> factory class, factory symbol, etc). >> (define-abstract-factory gui-factory >> (window pane button textfield)) >> (define-factory x11-factory gui-factory >> (x11-window x11-pane x11-button x11-textfield)) >> (define-factory x11-factory gui-factory >> (macos-window macos-pane macos-button macos-textfield)) >> (defparameter *gui-factory* (make-factory 'x11-factory)) >> >> [...] >> In effect, the abstract factory meta design pattern is thus implemented in >> lisp as a define-abstract-factory macro, and the concrete abstract factory >> design pattern as a define-factory macro. > > > I should add that while defining such macros may seem useless given the small > about of boilerplate they would cover, they offer the advantage of providing > an abstraction, that would let you change easily the implementation at a > later time (either to add features, or for optimization reasons, etc). >
Thanks for your thorough answer. Need a bit of time to fully go through it. Manfred
