From: Todd Benson <caduceass@...>
Date: 2007-08-30T23:22:35+09:00
Subject: Re: How to make an array of hashes to a single array with all the values of these hashes ?

On 8/30/07, kazaam <kazaam@oleco.net> wrote:
> thanks guys! dimas solution showed me my error
>
>         myvalue.each {|arr|  @my_new_array << arr.values }
>         puts @my_new_array
>
> is working if I initialize @my_new_array = [] before like dima did with a = [] but two questions:
>
> Why is a local variable my_new_array not working but just @ instance or $ global variables and why do I have
> initialize this varriable? I think you don't need this in ruby? But without initialisation it just shows nil?


It's about scope.  I'm sure the veterans here can give you a thorough
explanation, (and please pipe in here, because I don't want to spread
disinformation), but basically the block tries to retain its own scope
as best it can (from what I understand).  So, new variables that are
not "swallowed" from the scope outside of the block need to be
initialized, and those initialized within the block don't get outside
of the block (what happens in Vegas stays in Vegas, blah blah).

Simple example...

irb(main):001:0> a = 1,2,3,4
=> [1, 2, 3, 4]
irb(main):002:0> a.each { |i| b = i } #nothing happens here outside of
the block for b
=> [1, 2, 3, 4]
irb(main):003:0> b
NameError: undefined local variable or method `b' for main:object


Here's one that will make you think a little that is somewhat OT, but
demonstrates namespace danger...

irb(main):001:0> a = 1,2,3,4
=> [1, 2, 3, 4]
irb(main):002:0> a.inject{ |s, a| s + a }
=> 10
irb(main):003:0> a
=> 4

The a is not the accumulator, but it has changed even though the
method doesn't have a ! following it.  These are the small
idiosyncrasies that we have to be aware of with namespace and scope.

I may not be understanding your question, though.

> kazaam <kazaam@oleco.net>

Todd