Common Lisp Object System
是在阅读wikipedia Covariance and contravariance (computer science)时，其中关于CLOS的multiple dispatch的描述吸引了我的注意:
Another language feature that can help is multiple dispatch. One reason that binary methods are awkward to write is that in a call like
a.compareTo(b), selecting the correct implementation ofcompareToreally depends on the runtime type of bothaandb, but in a conventional OO language only the runtime type ofais taken into account. In a language with Common Lisp Object System (CLOS)-style multiple dispatch, the comparison method could be written as a generic function where both arguments are used for method selection.
multiple dispatch是一个非常有用的特性，值得注意。
wikipedia Common Lisp Object System
The Common Lisp Object System (CLOS) is the facility for object-oriented programming which is part of ANSI Common Lisp. CLOS is a powerful dynamic object system which differs radically from the OOP facilities found in more static languages such as C++ or Java.
CLOS is a multiple dispatch system. This means that methods can be specialized upon any or all of their required arguments. Most OO languages are single-dispatch, meaning that methods are only specialized on the first argument.
Features
CLOS is a multiple dispatch system. This means that methods can be specialized upon any or all of their required arguments. Most OO languages are single-dispatch, meaning that methods are only specialized on the first argument.