From: Rob Biedenharn <Rob@...>
Date: 2007-02-15T03:53:07+09:00
Subject: Re: Drying a ternary condition

On Feb 14, 2007, at 1:33 PM, sur max wrote:
>> On 2/14/07, Tim Pease <tim.pease@gmail.com> wrote:
>>> On 2/14/07, Marcello Barnaba <bofh@softmedia.info> wrote:
>>> > How would you write the following statement:
>>> >
>>> > klass.send((ARGV[0] || :up).to_sym == :up ? :up : :down)
>>>
>>> ARGV[0] ? klass.send(:up) : klass.send(:down)
>>>
>>> Blessings,
>>> TwP
> klass.send(ARGV[0] ? :up : :down)
> --  
> sur
> http://expressica.com

Since neither of those does the same as the OP's statement, they  
can't be right.  I'd argue that the statement is pretty DRY already.   
Your original code says: "If the first argument is "up" or false,  
call klass.up, otherwise call klass.down"

The other responders would call klass.down when ARGV[0] is false/ 
nil.  Also you can't call nil.to_sym (as you probably learned from  
ARGV[0].to_sym raising a NoMethodError) or "".to_sym (ArgumentError  
for the empty string).

If there were more than two options, something like this might be  
helpful.

 >> m=Hash.new(:down).merge!({:up=>:up})
=> {:up=>:up}
 >> [ :up, :down, nil, :fred, "up", "down", "", "fred" ].each do |x|
?>     puts "#{x.inspect} => #{m[(x.to_sym rescue :up)].inspect}"
 >>   end
:up => :up
:down => :down
nil => :up
:fred => :down
"up" => :up
"down" => :down
"" => :up
"fred" => :down
=> [:up, :down, nil, :fred, "up", "down", "", "fred"]

So:

klass.send(Hash.new(:down).merge!({:up=>:up})[(ARGV[0].to_sym  
rescue :up)])

Yuck!  Stick with the simple ternary for your statement (although you  
might want to use the rescue trick instead of just ||).

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com