"I have a mind like a steel... uh... thingy." Patrick Logan's weblog.

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Sunday, March 25, 2007

Delegation and Inheritance

In 1986 Henry Lieberman presented at OOPSLA a really simple object system based on delegation to any other object rather than on inheritance through some fixed tree of definitions.

Confused looks led to friendly arguments, led to the Treaty of Orlando a year later. And then Self, etc. expanded on this, Newton Script, and Javascript. (But the wonder of it has been lost along the way. Javascript is getting "serious" by adding classes and type checking and so on. Bah. Forgive them for they know not...)

As long as we still care about objects then, here comes Ian Piumarta with his new one(s), er, two, no, one: "Pepsi" and "Coke". In a recent addition to Pepsi, Ian has delicately spliced the two worlds together...

Compared to inheritance, delegation is the more flexible and general of the two techniques. However, they both have their place within an object model: inheritance for sharing of implementation state (and the methods that act upon it) for a single prototype (within a hierarchy of related prototype families), and delegation for sideways composition of (independent and previously unrelated) prototypes into a single logical composite object. This is the position adopted (and implemented) for sideways composition of Pepsi objects.

1 comment:

Unknown said...

"""Javascript is getting "serious" by adding classes and type checking and so on."""

Corollary to Zawinski's Law:

"Every language attempts to expand until it turns into Java. Those languages which cannot so expand are replaced by ones which can. Those which do will eventually be replaced by ones that don't, for reasons obvious to everyone else."

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Portland, Oregon, United States
I'm usually writing from my favorite location on the planet, the pacific northwest of the u.s. I write for myself only and unless otherwise specified my posts here should not be taken as representing an official position of my employer. Contact me at my gee mail account, username patrickdlogan.