From: "Peña, Botp" <botp@...>
Date: 2008-09-26T18:56:03+09:00
Subject: Re: How does Array's each method change its elements ?

From: w wg [mailto:duzuike@gmail.com] 
#..
# a = ["how","are","you"]
# b = a.each { |x|  x <<  "-"  }
# puts a
# ["how-","are-","you-"]
# puts b
# ["how-","are-","you-"]
# 
# The array changed!
# 
# I want to know how does Array's each method (block) change 
# its elements ?

each just iterates on each element/object of the array. an array is just a container of objects (wc includes also arrays). if you use << or concat method, you change the object, ergo, you change the array too.

try array#map and just use simple + for concatenation, eg

> a
=> ["how", "are", "you"]

> c = a.map{ |x|  x +  "-"  }
=> ["how-", "are-", "you-"]

> a
=> ["how", "are", "you"]

> c
=> ["how-", "are-", "you-"]

also note, strings are mutable objects, but, numbers are not.
see,

> a=[1,2,3]
=> [1, 2, 3]

> b=a.each{|x| x+=1}
=> [1, 2, 3]

> a
=> [1, 2, 3]

> b
=> [1, 2, 3]

no change
the expression x+=1 seems to change the object pointed by var x. but no. a new object (eg 2) is now pointed by x, wc is outside of the array. ruby cannot change the object 1. for ruby, 1 is always 1. Since we did not do anything on the new objects 2,3,4, they just get lost/cleanuped. They were there before. You can print them if you're in doubt. But you can save them easily if you use array#map.

let's use again map

> b=a.map{|x| x+=1}
=> [2, 3, 4]

> a
=> [1, 2, 3]

> b
=> [2, 3, 4]

hth
kind regards -botp