For example, suppose there are two methods defined for width
as follows:
(defmethod width ((c character-class) &key font) ...)
(defmethod width ((p picture-class) &key pixel-size) ...)
Assume that there are no other methods and no generic
function definition for width. The evaluation of the
following form should signal an error because
the keyword argument :pixel-size is not accepted by the applicable method.
(width (make-instance `character-class :char #\Q)
:font 'baskerville :pixel-size 10)
The evaluation of the following form should signal an error.
(width (make-instance `picture-class :glyph (glyph #\Q))
:font 'baskerville :pixel-size 10)
The evaluation of the following form will not signal an error
if the class named character-picture-class is a subclass of
both picture-class and character-class.
(width (make-instance `character-picture-class :char #\Q)
:font 'baskerville :pixel-size 10)