From: Phlip <phlip2005@...>
Date: 2009-02-22T03:14:40+09:00
Subject: Re: why not check for nil?

Roger Pack wrote:
> matt neuburg wrote:
>> A post I ran across on a rails forum reads:
>>
>> "Warning! DO NOT test for nil! This is a very bad coding practice. You
>> can use "if obj", but do not use "if obj.nil?" or whatever."
>>
>> Is that generally true? Why? m.
> 
> because it might be false [not nil]?

Technically yes, but that admonition has more meanings (some of which may have 
escaped that original rails poster).

Consider this pattern:

   if @user
     render :partial => 'premium_content' # for logged-in users
   else
     render :partial => 'teaser_content' # for the great washed masses
   end

That is sloppy programming because it asks @user for its type (are you a 
logged-in user? or just a slovenly nil?)

The correct pattern is @user is never nil, and if no user is logged in, then it 
should hold a "Guest" object. Then User and Guest can provide different methods 
for the same messages (method names):

   render :partial => @user.content_template

That pattern collects many redundant 'if' statements into one place; that 
technique is the heart of all OO programming.

-- 
   Phlip