From: "Einar Magnús Boson" <einarmagnus@...>
Date: 2008-12-01T03:42:06+09:00
Subject: Re: Help me understand how this block works?


On 30.11.2008, at 18:27 , Brian A. wrote:

> Hello -
>
> I'm working through a tutorial and Ive come across a line of code  
> that I
> do not understand.  The program basically takes a roman number value  
> and
> converts it to its integer counterpart.
>
> Here is the line:
> roman_string.to_s.upcase.split(//).reverse.inject(0) do |memo, digit|
>
> If roman_string contains the value "IV", when we come to this line can
> you please explain what the 'inject' does?  When I step through it in
> debug mode, I can see it gets assigned '0'.  But how is the 'digit'
> populated?  How does it know it gets the 'V' first and subsequently  
> 'I'?
> Does it do this by default because the inject(0) populates the memo so
> the only variable left is digit?
>
> I tried to play around, by removing the '.inject(0)' and the 'memo' to
> see if I could understand what it was doing but to no avail.
>
> roman_string.to_s.upcase.split(//).reverse. do |digit| # program balks
> at this
>
> If you'd like me to post the whole program I could, but I didnt want  
> to
> clutter the post.
>
> Thank you.
> Brian A.
> -- 
> Posted via http://www.ruby-forum.com/.
>


Google "ruby iterators tutorial" and try typing

	ri Enumerable#inject

in the terminal.


einarmagnus