[erlang-questions] object vs. actor (Re: Massive Numbers of Actors vs. Massive Numbers of Objects vs. ????)

Miles Fidelman <>
Thu Mar 1 00:11:55 CET 2012

Raoul Duke wrote:
> hi,
> question: what is the difference between an actor and an object? i
> have seen so many different definitions of the things! the words seem
> to be heavily context-dependent.
My understanding (and how I differentiate):

- an object encapsulates state and methods, but is not "active" - 
depending on the environment, methods can be invoked by procedure call 
or message passing (it's a chunk of data bound to methods for 
manipulating that data)

- an actor also encapsulates state and methods, but is "active" - it's a 
running process that's listening for and responding to messages (it's a 

There are, of course, more formal definitions.  Hewitt is sort of the 
definitive source for defining the actor formalism.  Not sure who's his 
counterpart for objects.

What it always comes down to, for me, is flow of control.  Objects just 
sit there, until some thread winds through them, or until triggered by 
an event.  Actor based systems consist of massive numbers of 
concurrently executing processes.  Very different ways of thinking about 
things at a systemic level.

Of course these are only my views - your mileage may vary.

Miles Fidelman

In theory, there is no difference between theory and practice.
In practice, there is.   .... Yogi Berra

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