From: Omer Raviv <omerraviv@...>
Date: 2006-06-30T18:07:03+09:00
Subject: Re: Symbol#to_proc is just so beautiful

Berger, Daniel wrote:

> There must be a way to ditch that '&' somehow.  I'd prefer this:
> 
> [1,2,3].all?(:positive?)


What you are suggesting is basically an expansion of something that was 
suggested in RCR50 and rejected. 
(http://www.rcrchive.net/rejected.html#rcr50)

I like the idea too.  It would be even better if you could also pass 
parameters along.

Here are a few more examples:

[1,2,3].any?(:>, 4)

[1,2,3].map(:*, 4)   #->  [4,8,12]

people.collect(:name)

people.select(:retired?)

people.sort_by(:age)

favorite_numbers.select(:between?, 100,200)

people.each(:give_compensation, 50)


Here's the implementation:
# enumerable-rcr50.rb
class Array

    enumerable_methods = [:each,:select, :find_all, :map, :collect, 
:any?, :all?,
                          :sort_by, :reject, :detect, :find, :find_all]
                        # max_by, min_by, partition_by can be added in 
Ruby 1.9
    for method_name in enumerable_methods
        old_method_name = "old_" + method_name.to_s
        module_eval %Q{
            alias_method :#{old_method_name},  :#{method_name}
            def #{method_name}(message = nil, *args, &block)
                block ||= Proc.new { |e| e.send(message, *args) }
                if message or block_given?
                    #{old_method_name}(&block)
                else  # method was called without passing any 
parameters, nor a block
                    #{old_method_name}
                end
            end
        }
    end

    alias_method(:do, :each)
    alias_method(:in_order_of, :sort)
end


Basically, if the callers passes a block, the original method is called. 
If he specifies a message and some arguements, they are converted into a 
block and passed to the original method. If he gives both, the block is 
used and the message is ignored. If neither is given (as in: 
[1,2,3].map), the original method is called with no parameters.

Take note that :detect (and its alias :find) accept an additional 
parameter (representing what should be returned if nothing is found), so 
changing them WILL break existing code.

Now, I need help. As you may notice - the above only extends Array. If 
you change "class Array" to "module Enumerable" in the above code, it 
turns out that Ruby (1.8.4) refuses to let you override methods such as 
map, while at the same time, "any?" and "all?" work fine. Anyone got a 
clue as to how I could fix this?

P.S. for other approaches to this problem, see the Higher Order 
Messaging in Ruby articles by Nat Pyrce 
(http://nat.truemesh.com/archives/000535.html), the Junction library, 
and Ruby Facets.

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