From: daz <dooby@...10.karoo.co.uk>
Date: 2003-07-16T14:45:12+09:00
Subject: Re: How to reduce Ruby runtime error?


"Xiangrong Fang" <xrfang@hotmail.com> wrote:

>
> if a[1].upcase == "GOOD" then...
>
> a[1] is nil, and you can't do "upcase" with it!
>

I'd use
         (a[1] ||'').upcase

||'' over 'to_s'
||0  over 'to_i'

 etc., to handle nil values.

>
> Is it possible to "overload" the Nil class so that it is polymophic?
> for example, if the method upcase is called, nil act like string,
> if the expression a = 2 + nil is executed, nil act like zero?
> That will be fantastic.
>

That would be _different_.
I wouldn't do it, even in the privacy of my own home :)


irb(main):001:0> dat = [3, 4, nil]
=> [3, 4, nil]
irb(main):002:0> dat.map {|z| z + 1}
NoMethodError: undefined method `+' for nil:NilClass

irb(main):003:0> dat.map {|z| (z ||0) + 1}
=> [4, 5, 1]


irb(main):004:0> dat = ['three', 'four', nil]
=> ["three", "four", nil]
irb(main):005:0> dat.map {|z| z + '*'}
NoMethodError: undefined method `+' for nil:NilClass

irb(main):006:0> dat.map {|z| (z ||'') + '*'}
=> ["three*", "four*", "*"]


daz