From: Jim Weirich <jim.weirich@...>
Date: 2011-01-29T12:28:55+09:00
Subject: [ruby-core:34968] Re: [Ruby 1.9-Feature#4326] Fiber should respond to call() and []


On Jan 28, 2011, at 7:45 PM, Charles Oliver Nutter wrote:

 > So...there are three possibilities:
> 1. subroutines are a specialization of coroutines. Then it's perfectly
> valid for subroutines to define things coroutines do not.
> 2. subroutines are equivalent to coroutines. Then coroutines should
> add [] and call and subroutines should have resuming/yielding
> capabilities.
> 3. coroutines are a specialization of subroutines. Then coroutines
> should add [] and call, and we're done. And Knuth is wrong.

I wouldn't say Knuth is wrong, but a natural language "is-a" is not  
always an indication of subtype (c.f. the square/rectangle paradox  
where a square is-a rectangle, but having square inherit separate  
set_width/set_height methods from rectangle would be wrong).

So, I would add a 4th possibility:

4. Subroutines, fibers, Method objects, and continuations (in MRI) are  
all subtypes of Callable, i.e. an object that will execute some code  
when "called".  In this view, all of the above should be LSP with the  
"Callable" protocol (i.e. implement call/[]).

-- 
-- Jim Weirich
-- jim.weirich@gmail.com