From: Mike Austin <mike_ekim@...>
Date: 2010-06-06T05:55:06+09:00
Subject: Re: Processing (potentially) nil method without using nested if

On Jun 5, 1:33 pm, Ben Vishny <bvis...@gmail.com> wrote:
> Hi all,
>
> really stupid question. How can I evaluate the following code without
> using a nested if.. then statement?
>
> if parent.respond_to? "children"
>     if parent.children.size != 0
>         puts "Has children"
>    end
> end
>
> Ideally I'd like to do:
>
> if parent.respond_to? "children" && parent.children.size != 0
>    puts "Has Children"
> end
>
> But I get an error if parent.children is undefined. Isn't there a way of
> stopping if the first condition is false?

Hi Ben,

Because of precedence rules, your above code is being parsed as:

if parent.respond_to?("children" && parent.children.size != 0)
   puts "Has Children"
end

"&&" and "and" have different precedence, and when leaving out
parenthesis in function calls, it's not as clear as to what's going on
(to the reader/writer).  In this case, you can surround the two
expressions with parenthesis, or use "and" instead.

http://blog.jayfields.com/2007/08/ruby-operator-precedence-of-and-which.html

Mike

> Thanks,
>
> Vish
> --
> Posted viahttp://www.ruby-forum.com/.