From: Doug Edmunds <dae_alt3@...>
Date: 2001-03-20T09:40:02+09:00
Subject: [ruby-talk:12895] differences between range and array

This code comes from the online code examples for
the Programming Ruby book

#==== code start ========
  module Inject
    def inject(n)
       each do |value|
         n = yield(n, value)
       end
       n
    end
    def sum(initial = 0)
      inject(initial) { |n, value| n + value }
    end
    def product(initial = 1)
      inject(initial) { |n, value| n * value }
    end
  end

class Array
   include Inject
end

class Range
   include Inject
end

# ===== code end =======

I saved that code as "test.rb"
then opened irb and typed include "test.rb".

Next I typed each of the following lines,
I get immediate results, fine:
[ 1, 2, 3, 4, 5 ].sum
[ 1, 2, 3, 4, 5 ].product
(1..5).sum
(1..5).product
('a'..'m').sum("Letters: ")

I typed these into irb, and they work:
p [ 1, 2, 3, 4, 5 ].sum
p [ 1, 2, 3, 4, 5 ].product

I type these into irb, they generate errors:
p (1..5).sum
p (1..5).product
p ('a'..'m').sum("Letters: ")


I added those lines to the test.rb file
to see what happens using the ruby interpreter:

%> ruby test.rb

These work, but produce no output:
[ 1, 2, 3, 4, 5 ].sum
[ 1, 2, 3, 4, 5 ].product
(1..5).sum
(1..5).product
('a'..'m').sum("Letters: ")

These also work  (array):
p [ 1, 2, 3, 4, 5 ].sum
p [ 1, 2, 3, 4, 5 ].product

but these don't (similar to irb):
p (1..5).sum   #generates an error
p (1..5).product #generates an error
p ('a'..'m').sum("Letters: ") #generates an error

However, this 2 step process works for the range:
aa = (1..5).sum
bb = (1..5).product
cc = ('a'..'m').sum("Letters: ")
p aa
p bb
p cc

What is different about how ranges and arrays process
this code, that p /array/ works but p /range/ doesn't?

#thanks

-- doug edmunds
19 March 2001