Re: print comparison

On Thu, Feb 10, 2011 at 8:35 AM, Mario Ruiz <[e-mail]> wrote:

> is it possible to print the comparison given as parameter in a method?
>
> something like this:
>
> mi(4==3)
> def mi(param)
>  I want to know here that the param was 4==3
> end
>
>
> I know that I could pass mi("4==3") and in the method use eval(param)
> but that's not possible in my case, I need to give a real comparison.
>
>
Why isn't it possible? I'll assume because you aren't dealing with literals,
so you need to pass the references to the actual objects. If so, you could
also pass the binding:



Person = Struct.new :name , :age do
  def <=>(person)
    age <=> person.age
  end
  include Comparable
end

bill = Person.new 'Bill' , 25
jenn = Person.new 'Jenn' , 17
carl = Person.new 'Carl' , 25



def mi( comparison , binding )
  log comparison
  eval comparison , binding
end

alias :log :puts


# binding: http://ruby-doc.org/core/classes/Kernel.html#M001448
mi "bill == jenn" , binding # => false
mi "bill == carl" , binding # => true
mi "jenn == carl" , binding # => false

# logged:
# >> bill == jenn
# >> bill == carl
# >> jenn == carl




And as always, with eval, be careful: know where your input code is coming
from, and be sure you can trust that source.