From: Brian Candler <B.Candler@...>
Date: 2002-11-14T19:16:51+09:00
Subject: Re: Newbie Question.

On Thu, Nov 14, 2002 at 01:29:51AM +0900, montana wrote:
> Simple Newbie question. I kind of understand this whole block thing.
> 
> 3.times {|i| puts i}
> 
> Bassically this is similar to 
> 
> a for statement in other languages.
> 
> What throws me off is the 
> 
> something do |line|
>   #process something and line here
> end
> 
> Is this correct? You take some object named something and process it's values in the do-end statement using the variable list??

The curly brackets and do..end are actually identical (apart from their
precedence when being parsed). So you can write either:

3.times {|i| puts i}

or

3.times do |i|
  puts i
end

In both cases, you are calling method "times" of the number 3, and passing a
block of code. The number 3 executes this code block 3 times. On each
iteration it replaces |i| with the index value, from 0 to 2.

[Note that although irb shows "0 1 2 3", the loop is only executed three
times with indexes of 0 to 2. 3 is the final value returned by the
expression, and irb prints it]

The idea of a number doing work for you might seem like a strange way of
doing things, but it gets clearer when you ask an Array to execute some code
for each of its elements:

a=["hello","to","you"]
a.each {|i| puts i}

Other objects respond to 'each', including Range, which gives you something
closer to a for loop:

(1..10).each {|i| puts i}

For a good explanation see
http://165.193.123.250/book/tut_containers.html

(that's www.rubycentral.com but its DNS is broken)

Regards,

Brian.