"Singletons" package on SM
avi at beta4.com
Thu Dec 4 00:42:22 UTC 2003
I've just placed a 15 minute hack on SM that might be useful to some
people. It allows for instance-specific behavior, or what's nicely
termed "singleton methods" in Ruby. I'm interested in comments. From
the SM description:
This package adds the #becomeSingleton method to Object, which will
transform the receiver into an instance of a new, anonymous subclass of
its original class. This lets you add or redefine methods on an
This is intended to be used primarily for delegation - replacing a
method with a block or a message send to another object. The methods
#to:run:, #to:send:to:, and #delegate:to: are provided for this
purpose. The following three calls are all equivalent:
x delegate: #foo: to: someOtherObject.
x to: #foo: send: #foo: to: someOtherObject.
x to: #foo: run: [:arg | someOtherObject foo: arg].
In all three cases, sending #foo: to x will end up forwarding the
message to someOtherObject.
My expectation is that this might be useful as a replacement for
specifying pluggable behavior with block inst vars or target/selector
pairs, particularly for UI classes. Rather than explicitly putting in
hooks for pluggablity, a well factored object can be customized from
the outside without its knowledge, by overriding existing methods -
particularly those that are #subclassResponsibility - but without going
to the trouble of adding a named subclass for each use.
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