Previous: , Up: Components   [Contents][Index]


6.2.3 Creating new component types

New component types are defined by subclassing one of the existing component classes and specializing methods on the new component class.

FIXME: this should perhaps be explained more throughly, not only by example ...

As an example, suppose we have some implementation-dependent functionality that we want to isolate in one subdirectory per Lisp implementation our system supports. We create a subclass of cl-source-file:

(defclass unportable-cl-source-file (cl-source-file)
  ())

A hypothetical function system-dependent-dirname gives us the name of the subdirectory. All that’s left is to define how to calculate the pathname of an unportable-cl-source-file.

(defmethod component-pathname ((component unportable-cl-source-file))
  (let ((pathname (call-next-method))
        (name (string-downcase (system-dependent-dirname))))
    (merge-pathnames*
     (make-pathname :directory (list :relative name))
     pathname)))

The new component type is used in a defsystem form in this way:

(defsystem :foo
    :components
    ((:file "packages")
     ...
     (:unportable-cl-source-file "threads"
      :depends-on ("packages" ...))
     ...
    )