Ruby - Singleton methods
| | Ruby user's guide | Singleton methods | |
The behavior of an instance is determined by its class, but there
may be times we know that a particular instance should have special
behavior. In most languages, we must go to the trouble of
defining another class, which would then only be instantiated
once. In ruby we can give any object its own methods.
ruby> class SingletonTest
| def size
| print "25\n"
| end
| end
nil
ruby> test1 = SingletonTest.new
#<SingletonTest:0xbc468>
ruby> test2 = SingletonTest.new
#<SingletonTest:0xbae20>
ruby> def test2.size
| print "10\n"
| end
nil
ruby> test1.size
25
nil
ruby> test2.size
10
nil |
In this example, test1 and test2 belong to
same class, but test2 has been given a redefined
size method and so they behave differently. A method
given only to a single object is called a singleton method.
Singleton methods are often used for elements of a graphic user
interface (GUI), where different actions need to be taken when
different buttons are pressed.
Singleton methods are not unique to ruby, as they appear in CLOS,
Dylan, etc. Also, some languages, for example, Self and
NewtonScript, have singleton methods only. These are sometimes
called prototype-based languages.
